This is the large clutch case gasket that is made to a special thickness.
Many companies who copy these gaskets are not aware that the gasket thickness and consistency is important as it affects the clearance on the idler gear shimming. This one is spot on. measures 30 thou or 0.77mm.
For the latest type generation of gasket material specially made for engine and gearbox we recommend using Klinger material
GUG705563GM.
Klinger material was used on the last 96 on Minis by Rover to overrcome leaks that might have been subject to warranty claims and expence.
Never use sealant on this application of gasket and only use 18lb.ft