We always called them "Clutch facings".
The important thing is not so much the length as whether the front of the
bearing is appropriate for a diaphragm clutch as opposed to a coil-spring
clutch with actuating arms. For some reason they prefer to specify the
clutches by brands rather than whether they are diaphragm or coil spring.
The coil spring clutch does better with a throwout bearing with a flat front
surface while the diaphragm clutch needs one with a rounded or toroidal
surface. Some of the throwout bearings have a cylindrical contact surface
that is about 3mm in wall thickness. These can wear a groove in the diaphragm
fingers and cause binding and jerky release. They used to be a sufficiently
standard part that you could go to any parts store and look at them before
buying. It has been so long since I bought one that I don't know if they
are that common any more.
BTW I have seen both brands (Borg & Beck and Fichtel & Sachs) on both the
coil spring and the diaphragm clutches, so specifying by brand is NOT enough!
--
George Downs Bartlesville, Heart of the USA!