Don

It’s McClellan’s patent, later made by M-F.  It came with the ball on the end,
or the breast pad, as in this one:

https://www.worthpoint.com/worthopedia/patented-stephen-mcclellan-
corner-bit-534091420">https://www.worthpoint.com/worthopedia/patented-stephen-
mcclellan-corner-bit-534091420

Ed Minch