Following on from this thread about BETD Onekey rings, anyone know what the Shimano centrelock cranks referred to here are?

It was a system used in the mid/late 90s where the crank had splines to take either a spider with 5-bolt compact-drive rings, or a spider with 4-bolt compact-drive inner and middle, and integrated outer ring(rivetted on).

So it falls into the category of ‘of historical interest’, then?

I wonder why they’ve not sacked it off and started doing SRAM spiderless instead.