Union Jubilee Clutch.

[Yorkie]

Surprised to see that the 'slipping belt cutch' on a lawnmower was patented as recently as 1977 in the US.

I don't know how that one differs from the normal slipping belt clutch on lawnmowers, but certainly in the early 1960s, as I recall they were fairly standard arrangements on motor mowers.

I'd assumed they went back donkeys years - aeons even. Simple enough, but very effective.

Best of luck in your experiementation and developement with the Jubilee clutch project Colin.