Connecting block with universal joint

Abstract

The utility model belongs to the technical field of medical instruments, and particularly relates to a connecting block with a universal joint, which comprises a joint and a plug screw, the joint is provided with a cylindrical through groove penetrating through a main body, one side wall of the cylindrical through groove is provided with a first opening, the first opening is communicated with the cylindrical through groove, the plug screw is matched with the first opening, and the plug screw is connected with the cylindrical through groove. A detachable universal spherical ring is arranged in the cylindrical through groove and comprises a limiting groove, the universal spherical ring comprises an upper spherical ring body and a lower spherical ring body which can be separated, the inner surface of the universal spherical ring body is matched with the rod, the outer surface of the universal spherical ring body is matched with the inner surface of the connector, and a second opening is formed in the other side wall of the cylindrical through groove. The clamping piece acts on the limiting groove of the universal spherical ring through the second opening, and the problem that the angle between the two nail rods is inclined due to spine curvature and double-rod reinforcement can be solved.

Description

Technical Field

[0001] The utility model belongs to the technical field of medical equipment and apparatus, in particular to a connecting block with a universal joint. Background Art

[0002] In the pedicle screw rod system in spinal fixation, the spinal fixation screw rod is used to maintain the curvature of the spine. In some cases, surgery is required to extend the original spinal fixation rod to increase the fixation range, which requires the use of a screw rod joint to increase the length of the spinal fixation screw rod. According to the needs of spinal fixation, there is often a certain angle between the two connected screw rods. The existing screw rod joint can usually only adjust the up and down offset angle of one of the screw rods, but cannot flexibly adjust its left and right offset angle. However, fine-tuning the left and right angles is required in the process of spinal fixation; in addition, the hinged structure between the two parallel joints is complex, which increases the volume of the joint and is easy to damage.

[0003] In another application, in orthopedic osteotomy surgery, double rod reinforcement is often required, and there may be a certain angle between the two rods according to needs. Utility Model Content

[0004] In view of the deficiencies in the prior art, the utility model provides a connecting block with a universal joint, which has the advantages of simple structure and easy use, and solves the problems mentioned in the above background technology.

[0005] The utility model provides the following technical solutions: A connecting block with a universal joint, comprising a joint and a screw plug, the joint being provided with a cylindrical through groove penetrating the main body, a side wall of the cylindrical through groove being provided with a first opening, the first opening being communicated with the cylindrical through groove, the screw plug being matched with the first opening, a removable universal spherical ring being provided in the cylindrical through groove, the universal spherical ring comprising a limiting groove, the universal spherical ring comprising a separable upper spherical ring and a lower spherical ring, the upper spherical ring and the lower spherical ring being able to be assembled into one, the inner surface of the universal spherical ring being matched with the rod, and the outer surface being matched with the inner surface of the joint, the other side wall of the cylindrical through groove being provided with a second opening, the locking piece acting on the limiting groove of the universal spherical ring through the second opening.

[0006] The universal spherical ring is designed as a split structure, divided into an upper spherical ring and a lower spherical ring. It can also be used for fine-tuning the rod size to make it larger than the diameter of the universal spherical ring, to ensure the close contact between the universal spherical ring and the rod. The screw plug plays a pressurizing role. The screw plug acts on the universal spherical ring through the first opening, so that the universal spherical ring remains in a specific position after the screw plug is pressurized. The traditional one-piece universal spherical ring uses the pressure given by the screw plug to deform the one-piece spherical ring and lock the rod. Therefore, there will be unnecessary stress problems, affecting the performance of the structure. The limit of the positioning piece is mainly to limit the rotation angle of the universal spherical ring.

[0007] A spherical surface with a diameter larger than the diameter of the cylindrical through groove is provided in the middle of the cylindrical through groove, and the outer surface of the universal spherical ring cooperates with the spherical surface. The purpose of the spherical surface structure in the cylindrical through groove is to ensure the stability of the rotation of the universal spherical ring after cooperating with the universal spherical ring. The split universal spherical ring structure can be easily inserted into the cylindrical through groove. At the same time, the size of the spherical surface in the middle of the cylindrical through groove is larger than the size of the cylindrical through groove, thereby limiting the movement in the Y direction and preventing the universal spherical ring from falling out. Compared with the traditional one-piece universal spherical ring, the split universal spherical ring has certain advantages in structure and assembly convenience.

[0008] The positioning piece and spherical surface design prevent the universal spherical ring from rotating randomly in the spherical surface.

[0009] The contacting surfaces of the upper spherical ring and the lower spherical ring are respectively provided with concave and convex groove structures to achieve matching constraint.

[0010] The limiting groove is formed by the concave-convex groove structure of the contact surface between the upper spherical ring and the lower spherical ring.

[0011] The universal spherical ring is provided with a limiter to control the distance between the upper spherical ring and the lower spherical ring along the z-axis direction.

[0012] The joint is a domino joint, the first openings are two axially parallel, the retaining members are two oppositely arranged on the joint, the universal spherical rings are two, the retaining members are pins, the retaining members include a stopper and a protrusion, the protrusion extends into the limiting groove for limiting, the second opening is a groove with an opening at one end, and a third opening is provided at the bottom of the groove, and the outer wall of the protrusion abuts against the inner wall of the third opening.

[0013] The longitudinal cross-section of the universal spherical ring is elliptical, and grooves are provided on the inner and outer surfaces of the universal spherical ring to increase friction, so that the universal spherical ring clamps the rod more firmly, and a gap is left between the protrusion and the limiting groove for adjusting the angle of the rod.

[0014] The stopper is a cylindrical pin, and the cylindrical pins are arranged on both sides of the spherical ring convex block near the second opening. The spherical ring convex block is provided with a pin hole, and the pin hole and the cylindrical pin are matched, and one end of the cylindrical pin is placed in the pin hole and the other end protrudes from the pin hole.

[0015] The stopper of the locking piece determines the position of the locking piece on the joint, and the protrusion extends into the limiting groove in the joint. The locking piece plays a limiting role. First, it prevents the universal spherical ring composed of the upper spherical ring and the lower spherical ring from excessively rotating in the cylindrical groove and disengaging from the joint; second, the gap between the front and rear surfaces of the protrusion and the limiting groove can constrain and control the rotation angle of the combination of the universal spherical ring around the x-axis and y-axis; third, the gap on the z-axis between the upper and lower surfaces of the protrusion and the limiting groove can control the distance between the upper and lower ends of the universal spherical ring along the z-axis. In order to control the distance between the middle side of the upper and lower spherical rings along the z-axis, the limiting thing works together with the locking piece to facilitate the insertion of the rod.

[0016] The limiting member is a limiting column, one end of which protrudes from the upper edge of the spherical ring convex block and is within the range of the limiting groove. Whether the limiting member is a cylindrical pin or a limiting column, it can be detachable or integrally designed with the spherical ring convex block.

[0017] The protrusion of the locking member is cylindrical, and the cross section of the third opening is cylindrical to match the protrusion.

[0018] Compared with the prior art, the utility model has the following beneficial effects:

[0019] The utility model designs a connecting block with a universal joint. The universal spherical ring is designed as a split structure, which is divided into an upper spherical ring and a lower spherical ring. Compared with the traditional integrated spherical ring, the split structure of the universal spherical ring can make the contact surface between the universal spherical ring and the rod more complete when pressure is applied through the screw plug, and the locking effect is better. It also avoids the stress problem caused by the integrated universal spherical ring when tightening. At the same time, the split structure can better reserve a limiting space, which is convenient for the pin to limit the rotation angle of the spherical ring. Therefore, the structure of the split universal spherical ring will be more reliable; the split structure can be used for fine-tuning of the rod size, which is larger than the diameter of the universal spherical ring, to ensure the close contact between the universal spherical ring and the rod, and has strong tolerance for fine-tuning of the rod size. The screw plug plays a pressurizing role, and the screw plug acts on the universal spherical ring through the first opening, so that the universal spherical ring remains in a specific position after the screw plug is pressurized. The positioning piece plays a limiting role, and the limiting piece can cooperate with the positioning piece to facilitate the insertion of the rod. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is an assembly diagram of a connection block with a universal joint according to a specific embodiment 1 of the utility model;

[0021] Figure 2 This is an exploded stereoscopic schematic diagram of a connection block with a universal joint in specific embodiment 1 of the utility model;

[0022] Figure 3 This is a front view of a full cross-sectional view of a connecting block with a universal joint in specific embodiment 1 of the utility model;

[0023] Figure 4 This is a left-side full cross-sectional view of a connection block with a universal joint in specific embodiment 1 of the utility model;

[0024] Figure 5 This is a top view of a full cross-sectional view of a connection block with a universal joint in specific embodiment 1 of the utility model;

[0025] Figure 6 This is a diagram of an assembly method of a connection block with a universal joint according to a specific embodiment 1 of the utility model;

[0026] Figure 7 This is a structural schematic diagram of a connection block with a universal joint according to a specific embodiment 2 of the utility model;

[0027] Figure 8 This is a structural schematic diagram of a connecting block with a universal joint according to specific embodiment 3 of the utility model.

[0028] In the figure: 1. Screw plug; 2. Connector;

[0029] 3. Pin; 4. Upper spherical ring; 5. Lower spherical ring; 6. Cylindrical pin; 7. First opening; 8. Second opening; 9. Third opening;

[0030] 21. Cylindrical through groove; 22. Spherical surface; 23. Limiting groove;

[0031] 31. Stop block; 32. Protrusion; 10. Rod; 11. Limit column. DETAILED DESCRIPTION

[0032] The following will be combined with the drawings in the embodiments of the utility model to clearly and completely describe the technical solutions in the embodiments of the utility model. Obviously, the described embodiments are only part of the embodiments of the utility model, not all of the embodiments. Based on the embodiments in the utility model, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the utility model.

[0033] In the prior art, the most commonly used connector is a rod connector. Since the original intention of the connector design is to reliably obtain a stable connection between the rods 10 and the rods 10, its structure is that two holes in the same direction are processed on a cube, and locking screws are processed on the hole walls. The two rods 10 to be connected are inserted into the two holes with their heads and tails facing each other, and then they are tightened and locked with locking screws to complete the connection.

[0034] Specific embodiment 1: Please refer to Figure 1-6 , a connection block with a universal joint, is mainly suitable for patients who undergo reoperation to extend the spinal fixation rod and corrective osteotomy, and can solve the problem of the angle tilt between the two nail rods 10 caused by the spinal curvature and the double rod 10 reinforcement. The doctor can appropriately adjust the angle of the two rods 10 according to the physiological curvature of the patient's spine and connect them through the connection block of the universal joint. This reduces the doctor's bending rod operation during the operation.

[0035] A connection block with a universal joint comprises a joint 2 and a screw plug 1. The joint 2 is a domino joint. The joint 2 is provided with a cylindrical through groove 21 that passes through the front and rear of the main body. The cylindrical through grooves 21 are two parallel ones. A first opening 7 is provided on one side wall of the cylindrical through groove 21. Figure 1 As can be seen, the first opening 7 is provided on the top of the domino joint, the axes of the two first openings 7 are parallel to each other, the first openings 7 are communicated with the cylindrical through grooves 21 below them, the screw plug 1 cooperates with the first opening 7, the screw plug is provided with an external thread, the inner wall of the first opening is provided with an internal thread, there are two screw plugs 1, one first opening 7 corresponds to one screw plug 1, a spherical surface 22 with a ball diameter larger than the diameter of the cylindrical through groove 21 is provided in the middle of the cylindrical through groove 21, and the outer surface of the universal spherical ring cooperates with the spherical surface 22.

[0036] A detachable universal spherical ring is arranged in the cylindrical through groove 21, and the longitudinal section of the universal spherical ring is elliptical. The universal spherical ring includes a limit groove 23, and the universal spherical ring includes a separable upper spherical ring 4 and a lower spherical ring 5, and the upper spherical ring 4 and the lower spherical ring 5 can be assembled into one body. The inner surface of the universal spherical ring cooperates with the rod 10, and the outer surface cooperates with the inner surface of the joint 2. The other side wall of the cylindrical through groove 21 is provided with a second opening 8, and the clamping member acts on the limit groove 23 of the universal spherical ring through the second opening 8. The clamping member is two pins 3 arranged opposite to each other on the joint 2.

[0037] The universal spherical ring is designed as a split structure, which is divided into an upper spherical ring 4 and a lower spherical ring 5. It can also be used when the size of the rod 10 is fine-tuned and becomes larger than the diameter of the universal spherical ring, thereby ensuring the close contact between the universal spherical ring and the rod 10. The screw plug 1 plays a pressurizing role. The screw plug 1 acts on the universal spherical ring through the first opening 7, so that the universal spherical ring remains in a specific position after the screw plug 1 is pressurized.

[0038] The contact surfaces of the upper spherical ring 4 and the lower spherical ring 5 are respectively provided with concave and convex groove structures to achieve matching constraints.

[0039] The limiting groove 23 is formed by the concave-convex groove structure of the contact surface of the upper spherical ring 4 and the lower spherical ring 5. The limiting groove 23 is formed by the concave-convex groove structure on the side of the universal spherical ring close to the second opening 8, and cooperates with the positioning member to play a limiting role. For a universal spherical ring assembly, the concave-convex groove structure on the other side away from the second opening 8 can be provided with or without the limiting groove 23, which does not affect the present design.

[0040] The positioning member includes a stopper 31 and a projection 32, wherein the projection 32 extends into the limiting groove 23 for limiting, the second opening 8 is a groove with one end opening, and a third opening 9 is provided at the bottom of the groove, the third opening 9 is communicated with the cylindrical through groove 21, and the outer wall of the projection 32 abuts against the inner wall of the third opening 9. One end of the projection 32 passes through the third opening 9 and enters the limiting groove 23, but the projection 32 cannot exceed the other end of the limiting groove 23, otherwise it will affect the abutment between the inner surface of the universal spherical ring and the rod 10.

[0041] The universal spherical ring is provided with a stopper to control the distance between the upper spherical ring 4 and the lower spherical ring 5 along the z-axis direction. In this specific embodiment, the stopper is a cylindrical pin 6, which is provided on both sides of the front and rear of the spherical ring protrusion 32 near the second opening 8. Figure 6 As shown, pin holes are provided on the front and rear faces of the spherical ring protrusion, and the pin holes cooperate with the cylindrical pins. One end of the cylindrical pin is placed in the pin hole, and the other end protrudes out of the pin hole. The cylindrical pin is inserted into the pin hole in the universal spherical ring through a tool after the universal spherical ring is placed in the cylindrical groove. After the cylindrical pin is installed, the universal spherical ring is supported, so that the universal spherical ring and the spherical surface in the cylindrical groove cooperate, thereby playing a limiting role.

[0042] The inner and outer surfaces of the universal spherical ring are provided with grooves to increase friction, so that the universal spherical ring can clamp the rod 10 more securely. A gap is left between the protrusion 32 and the limiting groove 23 to adjust the angle of the rod 10. Figure 3 It can be seen from the front cross-sectional view that there is a gap between the protrusion 32 and the limiting groove 23. The gap is the distance between the upper and lower surfaces of the protrusion 32 and the upper and lower walls of the limiting groove 23, and the distance between the front and rear surfaces of the protrusion 32 and the front and rear walls of the limiting groove 23. The pin 3 is stuck in the limiting groove 23. First, it prevents the assembly of the universal spherical ring from excessive rotation and disengaging from the domino joint; second, the gap between the front and rear surfaces of the protrusion 32 and the limiting groove 23 can constrain and control the rotation angle of the assembly of the universal spherical ring around the x-axis and y-axis; third, the gap on the z-axis between the upper and lower surfaces of the protrusion 32 and the limiting groove 23 can control the distance between the upper and lower end sides of the universal spherical ring along the z-axis direction.

[0043] The limiting member, namely the cylindrical pin 6 in this specific embodiment, is used to control the distance between the middle sides of the upper and lower parts of the universal spherical ring along the z-axis direction, and works together with the pin 3 to facilitate the insertion of the rod 10.

[0044] like Figure 3 , Figure 4 and Figure 5 As shown: The assembly relationship between the parts of the universal joint connection block. α, β represent the angles of the nail rod 10 adjusted up and down, and α1, β1 (α2, β3) represent the angles of the nail rod 10 adjusted left and right.

[0045] like Figure 6 As shown, the upper and lower parts of the universal spherical ring are fitted together through the concave-convex groove structure until the size of the circumscribed circle is smaller than the diameter of the cylindrical through groove 21 in the domino joint, and are placed in the domino joint in the direction shown in the figure, so that the outer spherical surfaces 22 of the upper and lower parts are matched with the spherical surface 22 in the domino joint. After the universal spherical ring is rotated 90 degrees, since the longitudinal cross-section of the universal spherical ring is an ellipse, as shown in FIG. Figure 6 After being inserted in the middle direction, it is rotated 90 degrees. The elliptical shape of the rotated universal spherical ring is larger than the diameter of the cylindrical through groove 21. The universal spherical ring is prevented from falling out by inserting the pin 3 and the cylindrical pin 6, thereby constraining the rotation angle of the universal spherical ring and controlling the distance between the upper and lower parts of the universal spherical ring along the z-axis direction.

[0046] When using, Figure 1-5 In the illustrated embodiment 1, the nail rod 10 is placed in the universal spherical ring, the universal joint connection block is adjusted according to the required inclination angle of the two nail rods 10, and by tightening the screw plug 1, the upper and lower parts of the universal spherical ring clamp the nail rod 10, thereby realizing the connection of the nail rod 10 with a certain inclination angle.

[0047] This patent uses a universal spherical ring structure in the universal joint connection block. For patients who need to undergo surgery to extend the spinal fixation rod, due to the physiological curvature of the human spine, this patent can better connect the angle between the two nail rods 10 caused by the extension of the spinal fixation rod. Compared with the traditional connection block, it can better preserve the physiological curve of the human spine after fixation. At the same time, in the orthopedic osteotomy surgery, it is also more convenient to connect the two rods 10, improving the efficiency of the operation. Specific embodiments

[0048] The difference between this specific embodiment and specific embodiment 1 is that the limiting structure of the distance between the middle sides of the upper and lower parts of the universal spherical ring (the upper spherical ring 4 and the lower spherical ring 5) along the z-axis direction is changed, and the cylindrical pin 6 is replaced by a limiting column 11.

[0049] The installation method is similar to that of the cylindrical pin in the specific embodiment 1. The limit post 11 is inserted into the groove of the universal spherical ring through a tool after the universal spherical ring is placed in the cylindrical groove. Figure 7 In the embodiment, an inverted T-shaped groove is provided near the upper edge of the spherical ring protrusion, and the limiting column 11 is also an inverted T-shaped structure. The vertical part in the inverted T-shaped of the limiting column is longer than the vertical part of the inverted T-shaped groove in the spherical ring protrusion. After the limiting column is installed, the universal spherical ring is supported, so that the universal spherical ring and the spherical surface in the cylindrical through groove cooperate, thereby playing a limiting role. Specific embodiments

[0050] The difference between this specific embodiment and specific embodiment 1 is that the limiting structure of the distance between the end sides and the middle sides of the upper and lower parts of the universal spherical ring along the z-axis direction is changed, the pin 3 is simplified and changed to a cylindrical shape, and the limiting is achieved by increasing the number of cylindrical pins. Specific embodiments

[0051] The difference between this specific embodiment and specific embodiment 1 is that the spherical surface 22 having a diameter larger than that of the cylindrical through groove 21 is eliminated, the longitudinal cross-section of the universal spherical ring is circular, and the angle of the universal spherical ring can be adjusted by the cooperation of the pin 3 and the cylindrical pin, thereby adjusting the angle of the rod 10. Specific embodiments

[0052] The difference between this specific embodiment and specific embodiment 2 is that the limit member and the universal spherical ring are an integrated structure, that is, the cylindrical pin is fixed to the concave-convex groove structure of the upper spherical ring 4 and the lower spherical ring, and is fixed to the front and back faces of the spherical ring protrusion near the second opening 8, and is used to limit the final falling position of the upper spherical ring, which cannot be lower than the position of the limit member. Specific embodiments

[0053] The difference between this specific embodiment and specific embodiment 3 is that the limit piece and the universal spherical ring are an integrated structure, that is, the limit column is fixed to the concave-convex groove structure of the upper spherical ring and the lower spherical ring, and is fixed to the front and back faces of the spherical ring protrusion near the second opening 8, and is used to limit the final falling position of the upper spherical ring, which cannot be lower than the position of the limit column.

[0054] In the description of the present utility model, it should be noted that the orientation or position relationship indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inside", "outside", etc. is based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present utility model and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation of the present utility model; the terms "first", "second", and "third" are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance. In addition, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present utility model can be understood according to specific circumstances. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements includes not only those elements but also other elements not expressly listed, or also includes elements inherent to such process, method, article, or apparatus.

[0055] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A connecting block with a universal joint, characterized in that: It includes a joint and a screw plug, the joint is provided with a cylindrical through groove running through the main body, one side wall of the cylindrical through groove is provided with a first opening, the first opening is communicated with the cylindrical through groove, the screw plug cooperates with the first opening, a detachable universal spherical ring is provided in the cylindrical through groove, the universal spherical ring includes a limiting groove, the universal spherical ring includes a detachable upper spherical ring and a lower spherical ring, the inner surface of the universal spherical ring cooperates with the rod, and the outer surface cooperates with the inner surface of the joint, the other side wall of the cylindrical through groove is provided with a second opening, and the locking piece acts on the limiting groove of the universal spherical ring through the second opening.

2. A connection block with a universal joint according to claim 1, characterized in that: A spherical surface with a diameter larger than that of the cylindrical through groove is provided in the middle of the cylindrical through groove, and the outer surface of the universal spherical ring matches the spherical surface.

3. A connection block with a universal joint according to claim 2, characterized in that: The contacting surfaces of the upper spherical ring and the lower spherical ring are respectively provided with concave and convex groove structures to achieve matching constraint.

4. A connection block with a universal joint according to claim 3, characterized in that: The limiting groove is formed by the concave-convex groove structure of the contact surface between the upper spherical ring and the lower spherical ring.

5. The connecting block with a universal joint according to claim 1, characterized in that: The universal spherical ring is provided with a limiter to control the distance between the upper spherical ring and the lower spherical ring along the z-axis direction.

6. A connection block with a universal joint according to any one of claims 1 to 5, characterized in that: The joint is a domino joint, the first openings are two axially parallel, the retaining members are two oppositely arranged on the joint, the universal spherical rings are two, the retaining members are pins, the retaining members include a stopper and a protrusion, the protrusion extends into the limiting groove for limiting, the second opening is a groove with an opening at one end, and a third opening is provided at the bottom of the groove, and the outer wall of the protrusion abuts against the inner wall of the third opening.

7. A connection block with a universal joint according to any one of claim 6, characterized in that: The longitudinal section of the universal spherical ring is elliptical, and grooves are provided on the inner surface and the outer surface of the universal spherical ring to increase friction. A gap is left between the protrusion and the limiting groove to adjust the angle of the rod.

8. The connection block with a universal joint according to claim 5, characterized in that: The limiting member is a cylindrical pin, and the cylindrical pins are arranged on both sides of the spherical ring protrusion close to the second opening. The spherical ring protrusion is provided with a pin hole, and the pin hole cooperates with the cylindrical pin. One end of the cylindrical pin is placed in the pin hole, and the other end protrudes from the pin hole.

9. The connection block with a universal joint according to claim 5, characterized in that: The limiting member is a limiting column, one end of which protrudes from the upper edge of the spherical ring protrusion and is within the range of the limiting groove.

10. The connection block with a universal joint according to claim 7, characterized in that: The protrusion of the locking member is cylindrical, and the cross section of the third opening is cylindrical to match the protrusion.

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