Belleville spring .... ^^
The new generation ....

What makes that spring so good over the coil springs of yesteryear is it's ability to give even pressure all the way around the 360 degrees of the clutch pack ...

The introduction of Norton's Commando series in 1968 had several great changes, including: "an entirely new clutch design from the earlier Norton twins. Designed by Laycock Engineering, the new design featured a diaphragm style spring,"
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"At launch, the very early models came with conventional multiplate wet clutches. But these were soon replaced in production with diaphragm clutches." http://www.classic-british-motorcycl...-commando.html