Stud support device

Abstract

The stud holder (42) includes a clamping portion defining three contact zones (18, 20, 22) designed to press against a lateral wall of a projecting part of the balance bridge. A first contact zone (18) is connected to a second contact zone (20) by a first portion (24A) and to the third contact zone by a second portion (26A) of the clamping portion. The first portion has a first stiffness at a second midpoint (30) of the second contact zone, relative to a first midpoint (28) of the first contact zone, which is greater than three times a second stiffness that the second portion has at a third midpoint (32) of the third contact zone relative to the first midpoint of the first contact zone. The first stiffness is advantageously seven times, and preferably twelve times, greater than the second stiffness.This results in a very precise radial positioning of the stud relative to the axis of rotation of the balance wheel.

Description

Technical field of the invention

[0001] The invention relates to a stud-carrying device incorporated into a watch movement, more precisely arranged on a balance bridge. Technological background

[0002] A stud holder is described in document FR 2368070. This stud holder is friction-mounted on a bearing surface (a protruding cylindrical part) of the balance bridge or on a shock-absorbing bearing support designed for the balance wheel. This stud holder includes a clamping element formed by a circular split ring, which comprises two symmetrical arms with a degree of elasticity to allow the stud holder to be friction-mounted on the balance bridge. A stud holder with a similar clamping element is also described in document CH 712854. The inner circle of the split ring has a diameter slightly smaller than that of the chimney or the circular part of the shock-absorbing bearing support intended to receive the stud holder, so that the two elastic arms spread apart slightly during mounting to ensure a tight fit and achieve the required friction.Since the inner circle has a smaller diameter than the diameter of the part on which it is mounted, the stud holder undergoes a slight displacement during assembly along the axis passing through the center of this circle and the midpoint of the opening between the elastic arms, in the opposite direction to that of this opening from the center. Generally, as shown in this document, the part of the stud holder to which the stud is attached is positioned on this axis opposite the opening of the split ring. Thus, the distance between the stud axis and the center of the inner circle of the split ring varies when the stud holder is mounted on the balance bridge. In fact, this distance increases, which poses a problem for the accuracy of the balance spring's attachment point to the balance bridge. It should be noted that this problem persists regardless of the angular position of the part to which the stud is attached relative to the center of the split ring.Indeed, in all cases, this part of the pin fixing undergoes the translation of a part of the split ring diametrically opposite to its opening which takes place along said axis passing through the center of this opening during the friction mounting of the pin holder on the balance bridge.

[0003] Document CH 604226 discloses a stud holder configured for bayonet mounting on a portion of the balance bridge and held in a specific angular position by friction between the stud holder and that portion. Specifically, the portion of the balance bridge in question is a part driven into a hole in the balance bridge plate and projecting above it. This part is designed to receive a balance wheel bearing. The ring has an internal flat which, following rotation of the stud holder to close the bayonet system, provides three-point clamping of a lateral wall of the aforementioned part by the ring to maintain angular positioning through friction. During the clamping rotation, the ring's flat undergoes a displacement relative to the ring's initial center, resulting in the same problem previously highlighted in document FR 2368070.Indeed, the eye bolt fixing area undergoes a small displacement in the plane of the eye bolt holder during a rotation of the eye bolt holder relative to the central axis of the driven part, which defines the axis of rotation of the balance wheel, to close the bayonet system and obtain tightening.

[0004] Document EP 1798609 also discloses a stud holder forming a bayonet system with a protruding portion of the balance bridge, as depicted in the figure 2of this document. The eye bolt holder is distinguished by three bosses located inside the ring surrounding the protruding part, which form the bayonet system. These three bosses contribute to the bayonet system by first allowing the eye bolt holder to be freely positioned at the correct level around the protruding part, and then closing the bayonet system by rotating the eye bolt holder into three respective lateral grooves machined into the protruding part. Hard friction is provided to prevent the eye bolt holder from having any play relative to the protruding part. However, no information is given regarding the elasticity of the two parts of the eye bolt holder between the central boss and the two end bosses, which have an opening between them.In fact, the elasticity of these two parts can be low, and the expected friction can also be low, since the friction only serves to prevent play and does not contribute to the axial retention of the eyelet holder, which is achieved by the bayonet system, nor to the angular positioning of the eyelet holder, since this angular positioning is achieved by a gooseneck return spring and a micrometer screw. It should be noted that, in the instruction provided in document EP 1798609, nothing suggests or leads to the conclusion that one of the two parts of the eyelet holder surrounding the protruding piece has a different elasticity than the other. Summary of the invention

[0005] The aim of the invention is to provide a stud holder that does not have the drawbacks of the prior art stud holders mentioned above. In particular, the invention aims to provide a stud holder that allows for very precise positioning of the stud within the overall plane of the stud holder, specifically a very precise and predetermined radial positioning relative to the axis of rotation of the balance wheel and hairspring.

[0006] To this end, the invention relates to a stud holder for mounting on the balance bridge of a mechanical watch movement, comprising a stud fixing portion and a clamping portion designed to clamp the side wall of a projecting part of the balance bridge or of a component mounted on the balance bridge. The clamping portion defines three contact areas designed, once the stud holder is mounted on the balance bridge, to press against the side wall of the projecting part or component. The first of these three contact areas is connected by a portion to a second contact area, which is adjacent to the first.The first part of the clamping section is rigid and has a first separation zone between the first and second contact areas. The first contact area is connected to the third of the three contact areas, which is also adjacent to the first contact area, by a second part of the clamping section that is elastic and has a second separation zone between the first and third contact areas. Once the stud holder is mounted on the balance bridge, the first and second separation zones are recessed from the side wall of the protruding part or component.In a general plane in which the clamping part extends globally, the first rigid part has a first stiffness at a second midpoint of the second contact zone, relative to a first midpoint of the first contact zone, which is greater than three times a second stiffness that the second elastic part has at a third midpoint of the third contact zone relative to the first midpoint of the first contact zone.

[0007] In an advantageous variant, the first stiffness is greater than seven times the second stiffness.

[0008] In a preferred variant, the first stiffness is greater than twelve times the second stiffness. Brief description of the figures

[0009] The invention will be described in more detail below with reference to the accompanying drawings, given by way of non-limiting examples, in which: There Figure 1Ais a top view of a hook holder according to a first variant of a first embodiment of the invention, and the Figure 1B is a top view of this eyelet holder mounted on a cylindrical section of a balance bridge; The Figure 2A is a top view of a hook holder according to a second variant of the first embodiment of the invention, and the Figure 2B is a top view of this eyelet holder mounted on a cylindrical section of a balance bridge; The Figure 3A is a top view of a hook holder according to a second embodiment of the invention, and the Figure 3B is a top view of this eyelet holder mounted on a cylindrical section of a balance bridge; The Figure 4A is a top view of a hook holder according to a third embodiment of the invention, and the Figure 4B is a top view of this stud holder mounted on a cylindrical part of a balance bridge. Detailed description of the invention

[0010] With reference to Figures 1A, 1B And 2A, 2B , we will describe below two variants of a first embodiment of a bolt holder according to the invention.

[0011] There Figure 1A shows a stud holder 2, according to a first variant, before its mounting on a balance bridge while the Figure 1BThe figure shows the stud holder 2 once mounted on a balance bridge 4 designed to receive it. The balance bridge 4 is conventionally found in a mechanical watch movement equipped with a balance wheel and hairspring whose balance wheel pivots in a bearing (these elements are not shown in the figures). This bearing is located in the center of a projecting part 6 of the balance bridge or of a component mounted on this balance bridge, and the outer end of the hairspring is held by a stud 9 which is fixed, in a known manner, notably by a lateral screw, in an opening 8 of a mounting part 10 of the stud holder. It should be noted that the opening can be replaced, notably by a slot, and that various alternatives can be considered by those skilled in the art for fixing the stud to the stud holder.

[0012] The stud holder includes a clamping portion 12 designed to clamp a side wall 16 of the projecting portion 6 or, alternatively, of a component mounted on this balance bridge. This projecting portion or component has a cylindrical or slightly frustoconical section whose cylindrical or frustoconical outer surface defines the side wall 16 and whose central axis 14 defines the axis of rotation of the balance wheel. The aforementioned component is, in particular, a component of a balance wheel assembly, including the stud holder in question, or a support for the bearing provided for the balance wheel and hairspring. When the stud holder 2 is mounted on a frustoconical portion, the circular cross-section of this portion increases with distance from the plate 5 of the balance bridge 4. The expression 'mounted on' does not necessarily mean that the component is above the plate of the balance bridge relative to the space provided for the balance wheel and hairspring.Indeed, in some designs, the pin holder can be arranged below the balance bridge board, on the balance-spiral side.

[0013] The clamping portion 12 defines three contact zones 18, 20, and 22 intended, once the stud holder is mounted on the balance bridge, to press against the lateral wall 16 of the projecting part 6. A first contact zone 18 of the three contact zones is connected to a second contact zone 20 of these three contact zones, which is adjacent to the first contact zone, by a first portion 24 of the clamping portion 12 that has a first separation zone 25 between the first and second contact zones. The first contact zone 18 is further connected to a third contact zone 22 of the three contact zones, which is also adjacent to the first contact zone 18, by a second portion 26 of the clamping portion that has a second separation zone 27 between the first and third contact zones.The first and second separation zones 25 and 27 are provided, once the pin holder 2 is mounted on the balance bridge 4, set back from the side wall 16 of the protruding part or piece.

[0014] In a general variant, the first contact zone 18 and the second contact zone 20 are tangent, in a general plane in which the clamping portion 12 extends globally, to a geometric circle 17 respectively at a first midpoint 28 of the first contact zone and at a second midpoint 30 of the second contact zone. In this general variant, the respective extents of the first and second contact zones are determined by the first and second points of contact to the geometric circle 17, which is tangent to the first and second contact zones at these first and second points of contact, which respectively define the first and second midpoints.

[0015] In the various embodiments shown in the figures, the three contact zones are planar. Advantageously, at least the first and second contact zones 18, 20 are planar and, in the general plane in which the clamping portion extends overall, orthogonal respectively to the two radii from the center 15 of the geometric circle 17, which pass respectively through the first and second midpoints 28, 30. Other variations are possible. In one particular variation, the first and second contact zones are concave, forming arcs of circles with the same radius and center as the geometric circle 17. In another particular variation, the contact zones are slightly convex, for example, forming arcs of circles with the same radius as that of the geometric circle.

[0016] In the first variant of Figures 1A and 1BThe first part 24 forms, in the first separation zone 25, a first circular arm with a rectangular cross-section, a width L1, and a mean radius R1 from the center 15 of the geometric circle 17. The first separation zone 25 extends over a first angular distance φ. The second part 26 forms, in the second separation zone 27, a second circular arm with a rectangular cross-section, a width L2, and a mean radius R2 from the center 15 of the geometric circle 17. The second separation zone 27 extends over a second angular distance θ.

[0017] According to the invention, in the general plane in which the clamping portion 12 extends overall, the first portion 24 has a first stiffness K1 at the second midpoint 30 of the second contact zone 20, relative to the first midpoint 28 of the first contact zone 18, which is greater than three times a second stiffness K2 that the second portion 26 has at a third midpoint 32 of the third contact zone 22 relative to the first midpoint 28 of the first contact zone, i.e., K1 > 3·K2. It should be noted that the stiffness considered is a bending stiffness and that the elastic constant of the first portion, and of the second portion respectively, is defined by the inverse of its bending stiffness.

[0018] According to an advantageous variant, the first stiffness K1 is greater than seven times the second stiffness K2, i.e. K1 > 7·K2.

[0019] According to a preferred variant, the first stiffness K1 is greater than twelve times the second stiffness K2, i.e. K1 > 12·K2.

[0020] In the example shown in Figures 1A and 1BThe width L2 = 0.55L1, the first angle φ = 68°, and the second angle θ = 110°. According to the laws of physics, the bending stiffness K varies with the width L to the third power, i.e., K ~ L 3 < , of the considered part (here, a circular arm), and also with its length to the third power, i.e., K ~ (R · ψ) 3 < , where R is the mean radius of the circular arm and Ψ is the angular distance of this circular arm. Considering, as a first approximation, only the two circular arms located in the two separation zones 25 and 27, we then obtain K1 = K2 · (1.5) 3 < · (1.8) 3 < , or K1 = approximately 20 · K2. Thus, the first stiffness K1 is approximately twenty times greater than the second stiffness K2. Therefore, in the example shown, the elasticity of the second part 26, more specifically of the second separation zone 27, is about twenty times greater than the elasticity of the first part 24, more specifically of the first separation zone 25.

[0021] In both variants of the first embodiment, the third midpoint 32 of the third contact zone 22 is substantially coincident, in the general plane in which the clamping part 12 extends globally, with a bisecting line 34 of a first angle α defined by the first and second midpoints 28 and 30 from the center 15 of the geometric circle 17 tangent to the first and second contact zones 18 and 20. Note that the adverb 'substantially' indicates in particular that this can be the situation envisaged before or after the mounting of the stud holder 2 on the balance bridge 4. In the first variant, the first angle α is substantially equal to ninety degrees (90°), the third midpoint 32 then presenting a second angle β relative to the first midpoint 28, from the center 15 of the geometric circle 17, substantially equal to one hundred and thirty-five degrees (135°).

[0022] Thanks to the characteristics of the stud holder 2 according to the invention, it is possible to mount the stud holder on the projecting part 6 of the balance bridge, ensuring very precise radial positioning of the opening 8, and thus of the stud 9, relative to the central axis 14 of the projecting part, which coincides with the axis of oscillation of the balance wheel and hairspring. Furthermore, precise positioning of the stud holder in a general plane, which is perpendicular to the axis of rotation 14 of the balance wheel, is achieved thanks to the two contact areas 18 and 20, which have an angular offset between them, advantageously between 60° and 120°, preferably 90°.Indeed, the first part 24, connecting the two contact zones 18 and 20, is designed with high rigidity relative to the second part 26, connecting the two contact zones 18 and 22, which exhibits sufficient elasticity so that, when the two parts 24 and 26 are separated, essentially only the contact zone 22 undergoes a displacement in the general plane of the stud holder relative to the contact zone 18. We can therefore speak of a first rigid part 24 and a second elastic part 26. It should be noted that the contact zone 22 is designed, before mounting the stud holder on the balance bridge, to be inside the geometric circle 17 which is tangent to the two contact zones 18 and 20.Thus, during assembly, substantially only the second elastic part undergoes elastic deformation and it is the first and second contact zones 18 and 20 which ensure the precise radial positioning of the eye 9 and also its precise positioning in the general plane of the eyelet holder once the eyelet holder is positioned angularly on the protruding part 6, given that the fixing part 10 of the eyelet is rigidly connected to the first rigid part of the clamping part 12.Indeed, as the first part 24 is rigid, the center 15 of the geometric circle 17 coincides with the central axis 14 of the protruding part 6 after the mounting of the stud holder on the balance bridge, given that the radius of the geometric circle 17, tangent to the contact areas 18 and 20, is provided to be equal to the radius of the protruding part 6 in the general plane considered, within the machining tolerances of the stud holder and the protruding part, tolerances which a person skilled in the art will make as small as possible for the machining technologies provided.

[0023] The eyelet holder 2 also includes a free part 36 which extends the first part 24 beyond the second contact zone 20. This free part has several functions, namely a safety function to prevent an impact from laterally dismantling the eyelet holder, a mounting function to allow a specific tool to momentarily move the third contact zone 22 away from the center 15, and an aesthetic function.

[0024] THE Figures 2A and 2BThis concerns a second variant of the first embodiment, which differs from the first embodiment essentially in that the first angle α and the second angle β are equal and each measure one hundred and twenty degrees (120°). In this case, the first angle φ (also called the first angular distance) is substantially equal to the second angle θ (also called the second angular distance). The various parts of the eyelet 42, which comprises a clamping portion 12A with a first portion 24A connecting the contact zones 18 and 20 and defining a first separation zone 25A, and a second portion 26A connecting the contact zones 18 and 22 and defining a second separation zone 27A, will not be described in detail again. It should be noted that the eyelet 42 does not include any additional free portion.

[0025] A calculation based on the example shown in Figures 2A and 2BThis gives the following result: The first stiffness K1 of the first part 24A, more specifically of the first separation zone 25A, is approximately five times greater than the second stiffness K2 of the second part 26A, more specifically of the second separation zone 27A. Therefore, in the example shown, the elasticity of the second part 26A, more specifically of the second separation zone 27A, is approximately five times greater than the elasticity of the first part 24A, more specifically of the first separation zone 25A. It should be noted that this value varies quite significantly with a relatively small variation in the ratio of the widths L1 and L2. Generally, the ratio between the first stiffness K1 and the second stiffness K2 is expected to be greater than three. Advantageously, this ratio is expected to be greater than seven, which can be easily achieved with the second variant. Preferably, the K1 / K2 ratio is expected to be greater than twelve.

[0026] THE Figures 3A and 3B show a second embodiment of a stud holder according to the invention. The parts of the stud holder 52 that are identical or similar to those of the first embodiment and that have already been described previously will not be described again here in detail. Reference should therefore be made to the description of the first embodiment for these identical or similar parts. Note that the letter 'B' appended to a number in a reference indicates that it is a part identical or similar to the one bearing that number as a reference in the first embodiment.

[0027] The eye bolt holder 52 includes a mounting portion 10 for an eye bolt 9, this mounting portion being integral with the first portion 24 of the clamping portion 12B. In particular, the mounting portion 10 is rigid and rigidly fixed to the first portion 24. The term 'rigidly fixed' does not imply that these two portions are initially separate parts that are fixed to each other, but rather that the mounting portion and the first portion together form a rigid part of the eye bolt holder. This rigid part defines first and second contact zones 18 and 20, which have a separation zone between them. This separation zone extends over a certain non-zero angular distance, advantageously between 60° and 120°, preferably approximately 90°. The clamping portion 12B also includes a second portion 26B connecting the first contact zone 18 to the third contact zone 22.Furthermore, the clamping portion defines a fourth contact zone 56 which, once the stud holder 52 is mounted on the balance bridge, is intended to press against the lateral wall 16 of the projecting portion 6 of the balance bridge (not shown) or of a part fixed to this balance bridge. This fourth contact zone 56 is adjacent to the second contact zone 20 and connected to this second contact zone by a third portion 54 of the clamping portion 12B, which has a third separation zone 55 between the second and fourth contact zones. The third portion 54 has a third stiffness K3 at a fourth midpoint 58 of the fourth contact zone, relative to the second midpoint 30 of the second contact zone, which is less than one-third of the first stiffness K1 of the first portion 24. In a preferred embodiment, the first stiffness K1 is greater than seven times the third stiffness K3, i.e., K1 > 7·K3.Thus, like the second part, the third part 54 is elastic.

[0028] Doubling the second elastic section with the third elastic section increases the total clamping force of the stud holder on the protruding part 6. The width L2 of the separation zones defined by the second and third sections 26B and 54 can be selected to determine the elasticity of these two sections. Like the third contact zone 22, the fourth contact zone 56 is located inside the geometric circle 17, tangent to the first and second contact zones 18 and 20 at their midpoints, before the stud holder is mounted on the balance bridge. To determine the total clamping force, the radial distance between the contact zones 22 and 56 can also be selected for the stud holder not yet mounted on the balance bridge.

[0029] In the variant shown, the third and fourth contact zones 22, 56 exhibit, in a general plane of the clamping portion 12B, axial symmetry with respect to a bisector line 34 of the first angle α defined by the angular offset between the first contact zone 18 and the second contact zone 20 from the center 15 of the geometric circle 17. More specifically, the second portion 26B and the third portion 54 are arranged symmetrically with respect to the bisector line 34, such that the angular distance θ1 of the second separation zone 27B is equal to the angular distance θ2 of the third separation zone 55 defined by the third portion 54. Thus, the second portion 26B and the third portion 54 of the clamping portion 12B exhibit axial symmetry with respect to the bisector line 34.

[0030] The second and third parts 26B and 54 have at their respective free ends two parts 62 and 64 which extend radially and which are provided to facilitate the mounting of the stud holder 52, around the protruding part 6 of the balance bridge, using a tool 66.

[0031] THE Figures 4A and 4BThese figures show a third embodiment of the invention. The eye bolt holder 72 has a much more complex shape than the eye bolt holders shown in the other figures. This eye bolt holder 72 serves several functions, which explains its particular shape. The eye bolt holder 72 comprises a fixing portion 10C for attaching an eye bolt 9 and a clamping portion 12C forming an open ring. As in the previous embodiments, the clamping portion or open ring is elastic not uniformly or over almost its entire angular range, but through the presence of at least one elastic portion. The clamping portion 12C comprises a first rigid portion 24C, connecting the first and second contact zones 18 and 20, and a second elastic portion 26C connecting the first and third contact zones 18 and 22.The first and second contact zones define an angle α between their respective midpoints, and the first and third contact zones define an angle β between their respective midpoints, which, in the example shown, is substantially equal to angle α. It should be noted that angles α and β have values ​​greater than 120° and approximately equal to 150°. This variant is therefore not preferred with regard to the benefits of the invention. However, since the first rigid part 24C has a high stiffness that is significantly greater than the stiffness of the second elastic part 26C, in particular more than twelve times greater, the angle α greater than 120° and equal to 150° allows for precise positioning of the fastening part 10C, rigidly connected to the first part 24C, and therefore of the eye pin 9 in the general plane of the eye pin holder once the latter is mounted on the balance bridge (not shown).

[0032] The first part 24C has a minimum width L1 Min at a single point, while the second part 26C has a circular arm of width L2, less than L1 Min and substantially equal to two-thirds of L1 Min, this circular arm extending over an angle Ω greater than 60°. Thus, substantially only the second part 26C undergoes elastic deformation during the mounting of the stud holder 72 around the projecting part 6 of the balance bridge. This mounting is carried out using a tool 66 which is inserted into an opening between the first and second parts of the clamping part 12C and allows their respective free ends to be separated.

Claims

1. A balance spring stud holder (2, 42, 52, 72) designed to be mounted on a balance cock of a mechanical horology movement and comprising a part (10) for attaching a balance spring stud and a clamping part (12, 12A, 12B, 12C) that is designed to be able to clamp a lateral wall of a protruding part of the balance cock or of a piece mounted on this balance cock; the clamping part defining three contact zones (18, 20, 22) designed, once the balance spring stud holder is mounted on the balance cock, to press against the lateral wall of the protruding part or piece, a first contact zone (18) of the three contact zones being connected by a first part to a second contact zone (20) of these three contact zones, which is adjacent to the first contact zone, characterised in that the first part (24, 24A, 24C) of the clamping part is rigid and has a first separation zone (25, 25A) between the first and second contact zones, the first contact zone being connected to the third contact zone (22) of the three contact zones, which is also adjacent to the first contact zone, by a second part (26, 26A, 26B, 26C) of the clamping part which is resilient and has a second separation zone (27, 27A, 27B) between the first and third contact zones, the first and second separation zones being designed, once the balance spring stud holder is mounted on the balance cock, to be recessed from the lateral wall of the protruding part or piece; and in that, in a general plane in which the clamping part extends overall, said first rigid part has a first stiffness at a second median point (30) of said second contact zone (20), relative to a first median point (28) of said first contact zone (18), that is three times greater than a second stiffness that said second resilient part has at a third median point (32) of said third contact zone (22) relative to the first median point of the first contact zone.

2. The balance spring stud holder according to claim 1, characterised in that the first stiffness is seven times greater than the second stiffness.

3. The balance spring stud holder according to claim 1, characterised in that the first stiffness is twelve times greater than the second stiffness.

4. The balance spring stud holder according to any of the preceding claims, characterised in that the third median point (32) of the third contact zone is substantially coincident, in a general plane in which the clamping part extends overall, with a straight line (34) bisecting a first angle (α) defined by the first and second median points from the centre (15) of a geometric circle (17) tangent to the first and second contact zones, at these first and second median points, or partially coincident with the first and second contact zones if the latter are machined in a circular arc with the same radius and same centre as said geometric circle.

5. The balance spring stud holder according to claim 4, characterised in that the first angle (α) is substantially equal to ninety degrees (90°), the third median point (32) then having a second angle (β) relative to the first median point, from the centre (15) of said geometric circle, substantially equal to one hundred and thirty-five degrees (135°).

6. The balance spring stud holder according to claim 4, characterised in that the first angle and the second angle are each equal to one hundred and twenty degrees (120°).

7. The balance spring stud holder according to claim 1 or 2, characterised in that the clamping part (12B) defines a fourth contact zone (56) that is designed, once the balance spring stud holder is mounted on the balance cock, to press against the lateral wall of the protruding part or piece, this fourth contact zone being adjacent to the second contact zone (20) and connected to this second contact zone by a third part (54) of the clamping part, which has a third separation zone (55) between the second and fourth contact zones; and in that the third part has a third stiffness at a fourth median point (58) of the fourth contact zone, relative to the second median point (30) of the second contact zone, which is less than one-third of said first stiffness of the first part.

8. The balance spring stud holder according to claim 7, characterised in that the first stiffness is seven times greater than the third stiffness.

9. The balance spring stud holder according to claim 7 or 8, characterised in that the third and fourth contact zones (22, 56) are, in a general plane in which the clamping part extends overall, axially symmetrical relative to a straight line (34) bisecting a first angle (α) defined by a first median point of the first contact zone and a second median point of the second contact zone from the centre (15) of a geometric circle (17) tangent to the first and second contact zones, at these first and second median points, or partially coincident with the first and second contact zones if the latter are machined in a circular arc with the same radius and same centre as said geometric circle.

10. The balance spring stud holder according to claim 9, characterised in that the second part (26B) and the third part (54) of the clamping part are axially symmetrical relative to said bisecting straight line (34).

11. The balance spring stud holder according to any of the preceding claims, characterised in that the first and second contact zones (18, 20) are planar.

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