PART NO.  SPL.PAGE  DESCRIPTION                                                            
AEH650     TC.A.5    Washer -distance (6) -(clutch to flywheel, engine, Twin Cam)

This page is for the part called "Spacer" in the following illustration. This may alternately be called Spacer, Ground Spacer, Distance Washer. Original specified thickness for this steel washer is 0.169-in or 4.3-mm. The ID should be minimal clearance for the 5/16" bolt (21/64" or 11/32"). The OD is (commonly) 11/16", but variation does not affect the function.

The Twin Cam clutch pressure plate assembly is somewhat different from those in the pushrod engine cars. It has slightly stronger pressure springs and also an intermediate plate called a "spider". In the picture below left you can see the spider plate through the center hole of the heavy pressure plate. In the picture below right there is a small arrow pointing to one of the nuts which secure the spider to the cover.
Friction lining on the Twin Cam driven disc is also a bit thicker than for the standard clutch disc. Collectively this makes the internal parts assembly stack a bit taller, so the clutch cover needs to be spaced a little back from the flywheel. This is the reason and function for the (6) spacer washers. This is unique to the Twin Cam clutch only. If a standard MGA or MGB clutch is installed, then these spacers must be deleted.