Chev 216 valve collets ( keepers)
 

I recently picked some nos DUFOR (Australian manufactured) exhaust valves for the Chev 216 engine, they also fit many other GM engines from that era. I have noticed that the DUFOR valves have a single wide groove for the collets . The GM originals I have seen have two narrow grooves for the collets .

Looks like GM changed the design of the stem groove and the collets at some point in time ? I think earlier style stems have the single wide groove but not sure.