ID Another Bolt Marking

A fellow member and friend passed along a PM to me asking about a Bolt he picked up over the weekend.

..... A bolt with some markings I can't find in any books. The bolt is the flat type with no marks on the right lug. The left lug is clearly marked: P M , and just under the left lug (in smaller font) is a B or an 8. Any ideas on who made the bolt?

Any Thoughts?

TIA,
Charlie-painter777

Could it be Plainfield Machine?

Charlie, I have a list of WWII suppliers that shows Pross Mfg. Co. as PM. Only problem is, I don't know what products they supplied - probably not bolts, though. - Bob

"B" under left lug may indicate an IBM (AOB) bolt. The AOB is sometimes stamped very faint on the right lug. If the bolt was refinished, the marking may have been removed. I know that some early AOB bolts had letters stamped on the left lug. One known example has a "VM" stamped on the left lug.

CA,
Nice Job !
He's looked closer and can see just the top half of the AOB on the right lug. Most of the AOB stamp missed the lug, splitting the A above the cross, the O in half along with the B. Looking at it upside down makes it look like a D or O, U then a V.
PM on the left lug. Still not sure if the marking under the left lug is a B or 8.
I'll try to get him to send along some pictures.

Thanks for your help, once again,
Charlie-painter777