I recently bought a few machinist chests full of tools and other goodies. I’m not a machinist myself, but I’m familiar with a lot of the tools associated with the trade. This piece is a smooth solid steel cylinder with four equal spaced holes bored completely through it. It measures approximately 5.5" long and 2.25" diameter. Weighs almost 4-1/2 lbs. The end has stamped “Feb. 48 Eddie Champ.” The other end is identical minus the engraving.
I suspect it might be a cylindrical square, but I’ve not seen examples quite like this. It came with a plastic sleeve.
The 4 through holes I would guess are mainly intended for weight reduction and to make the heat treament go a bit smoother, but also have a side benefit that you could run a bolt through them in order to attach it to a larger more complicated fixturing setup.