C-clamp

[HeelSpur]

The body of this was totally caked with rust so I soaked it in vinegar over-nite. This morning I wire brushed the rust off, which was very easy, it appears to be some kind of pot metal and the rest of it seems to be copper. A magnet sticks to it so its nut aluminumnumnum.
Searched AA for a P in a circle but didn't see it on the site.
What this clamp be used in a non-arching environment like gas or did it have another special use?

[Bill Houghton]

If a magnet sticks, there's some steel in it.

From here, the body of the clamp looks like cast iron.  Pot metal would be very light in weight.  If the magnet sticks to the body of the clamp, it's probably cast iron.  If it sticks to the screw, it's probably copper-coated steel.

Copper-coated screws are common for clamps intended for use in a welding environment.  Arc welding, particularly, will put off lots of hot splatter, and it won't stick as much to copper as to steel.

[HeelSpur]

If a magnet sticks, there's some steel in it.

From here, the body of the clamp looks like cast iron.  Pot metal would be very light in weight.  If the magnet sticks to the body of the clamp, it's probably cast iron.  If it sticks to the screw, it's probably copper-coated steel.

Copper-coated screws are common for clamps intended for use in a welding environment.  Arc welding, particularly, will put off lots of hot splatter, and it won't stick as much to copper as to steel.

Thanks Bill, I've been around welders all my life and never paid much attention to their clamps. Something I should of known I guess.

[Bus]

If you soak cast iron in vinegar or sandblast you get that aluminum pot metal looking finish.

[HeelSpur]

It has a seem that goes all the way around.

[rusty]

Cast iron / Cast mallable were common materials for making c-clamps...

P in a circle is a foundry mark, if I remember it was one of the ones that started as a brass founders mark (many did, the folks doing brass switched back and forth sometimes), can't recall whose tho....

[jimwrench]

 P in a circle was mark for Pittsburg Forging

[Bill Houghton]

It has a seem that goes all the way around.

Probably the pattern was laid in the drag (lower box of sand) halfway into the sand, then the cope (upper box) laid over and sand packed around.  You'd no doubt get a seam out of the two parts.  This doesn't always get ground off completely.