CRAMP wrench

[choonks13]

New to this site, but wondering if anyone has ever seen a CRAMP brand wrench.
I got one in a flea market outside of Phily. It is marked 3/8 but actual size is 11/16 so I know it is pre-1929 when SAE sizes were standardized. Thinking this might have come from a tool kit for a CRAMP engine. From William Cramp & Sons Ship & Engine Building Company but don't know for sure.

 

[2oolhound]

Welcome to GJ!

It sounds like british whitworth. Do a google search for whit worth to SAE chart for the specs.

 

[choonks13]

It does not convert to a Whitworth size. AlloyArtifacts.org has a standard opening size chart for Williams and Billing & Spencer (which some other mfg.s adopted) for back before they used SAE standards. When they used a lot of square head bolts and nuts. It sort of matches some of these although there is no wrench number just marked 3/8. I was really more interested if anyone could verify the maker, as i think this wrench is very rare and may have some value.

 

[Private Lugnutz]

It is marked 3/8 but actual size is 11/16.

It is marked for a United States Standard (U.S.S.) nut or bolt. U.S.S. bolts were heavier than S.A.E. standard bolts, and the nuts and heads on a U.S.S. bolt were a full 1/8" wider Across the Flats (AF) than the nuts and heads on an S.A.E. bolt of the same exact size. A 3/8" U.S.S. nut and bolt head was 11/16" AF and needed a wrench with an 11/16" milled opening to turn it. By comparison, a 3/8" S.A.E. standard nut and bolt head was 9/16" AF and needed a wrench with a 9/16" milled opening to turn it. See any early edition of Machinery's Handbook or the wrench to bolt/nut tables in any 1920's through 1940's tool mfgr catalog for all the wrench to nut/bolt sizes for each hardware standard that was in use well up through the 1940's (U.S.S., S.A.E., American Standard, and Hex Caps).

I don't know anything about Cramp & Sons Shipbuilders, but I suspect you could be on to something with your theory. I have never seen a CRAMP wrench before, and I have not seen it referenced here, Garage Gazette, AA, DATAMP, or any of the usual places for antique to vintage wrenches.

 

[choonks13]

Lugz, Thanks for the reference to the Machinery's Handbook.