Odd bit holder

Anybody have any idea what the original purpose of this bit holder may have been? Its something I had in with my metal working drawer of drill bits, files, reaming and tap tools.

Where it came from I don't recall. Maybe came out of the old electronics manufacturing plant way back when and was used on some assembly job there

The threaded mandrel is very similar to one for like a hole saw with the set screw to hold the bit, but it's not the right size. At least not for the saws I have. The hex shank portion must have been for a chuck though I would say

Wondering is it something out of the old machine shop, maybe made special :dunno: the hollowed nut is a bit odd but part of the assembly goes over the flats covers the set screw and tightens up against the smooth round base portion. Makes it really easy to hold too.

Got me

Attached Images
File Type: jpg bit 1.jpg (54.6 KB)
File Type: jpg bit 2.jpg (58.3 KB)
File Type: jpg bit 3.jpg (64.8 KB)