This 5 1/2" clutch disc fits the Tilton OT-III Single Disc Clutch (Part No. 173-60).
The 7/8"-20 spline pattern is the original spline for FF1600. If your car was converted from an FF2000 chassis, it may have the larger 1"x23 spline -- be sure to check before ordering.
Tilton's minimum recommended clutch disc thickness is 0.074" in single-disc clutches. New clutch discs measure 0.104" thick.