This is the same bearing supplied with our Tilton 3000-Series Hydraulic Release Bearing Assembly (Part No. TE 60-3000), as well as the original Tilton 300-Series HRB (Part No. 163-50).
The 52mm radiused contact face is perfect for clutches with a 1 7/8" diaphragm spring hole, including most AP racing clutches, QuarterMaster 7 1/4" Low Ground Clearance clutches, and Tilton 8 1/2" clutches. It can also be used with a Tilton 7 1/4" (OT-2), but pedal effort will be higher than with a 44mm bearing.