These were in a grab bag of tools. Not sure what they are. There is a JAPAN stamp. It appears to maybe be some sort of drill attachment but not sure. The three prongs are covered with rubber/silicon tips. The prongs are adjustable, if you turn the housing they move out/in. Also, the small post in the middle of the prongs appear as maybe something broke or sheered off.
This is a rare antique tool .
It is used for making large holes.
The only name that i know is an "adjustable hole saw."
Sorry for the sarcasm, it’s one of those days.
The silicone is just to cover sharp edges.
The broken center shaft is a drill bit.
I was going to say the same thing - the markings on the one prong are a dead giveaway.
metric I suspect - and it’s really only for drywall or a softer material. You can still get something like this today.