A setting gauge (G) determines the thickness of a spacer (22) which gives the correct setting for a pair of tapered roller bearings (B1, B2) that are mounted in opposition to accommodate relative rotation between machine components (S, H). The gauge has a base (50) which at one end fits against a surface (12) to which the spacer is to be applied, and at its other end holds one of the races (32) of the bearing (B2) remote from the other race (30) which remains in its operating position. In addition, the gauge has a pair of gauge elements (52, 54), one of which fits against a conical envelope along the remote race and the other of which fits against an identical conical envelope on the race which remains in its operating position, in effect, projecting the conical envelope defined by the in-place race out of the bearing to a remote location so that measurements may be taken from the bearing. The race which is remote during the measurements has a cylindrical surface (48) which is configured to fit another cylindrical surface (10) on one of the machine components (H) with an interference fit, and the gauge also measures the diameters of the two cylindrical surfaces so that the magnitude of the interference fit may be ascertained and its effect on the bearing compensated.