What is it for?

[OilyRascal]

Pulling this out of the Thorsen collection thread for a little more visibility.  I know what it is - it is a Thorsen Model 18 1/2" drive x 5/16" adapter.  What I don't know is what it's for.  I have never heard of a 5/16" drive, and I've not seen any 5/16" drive tools (thorsen or otherwise).  I do know that Thorsen was in the business of making specialty automotive tools at one point.  Appreciate any input you may have.

[EVILDR235]

I have several 5/16 to 1/4 inch adapters. I have no idea about any 5/16 drive tools.

EvilDr235

[Lostmind]

possibly to remove a drain or fill plug,trans or diff case ?

[john k]

I believe this is for engine work.  Oil gallery plugs in the engine block, block off pipe plugs, all have to be removed during overhaul, at least on the older engines, to get the passages cleaned out.   I can remember seeing a set of square drive male sockets in 3/8 or 1/2 in. drive. 

[amecks]

Is there a ball on the 5/16" end? If not it is likely for engine plugs as mentioned.
My grandfather had a set of Snap-On sockets that maybe were 5/16" drive. I only know they were too big for 1/4" drive and too small for 3/8" drive.
Al.

[FrankLee]

I really didn't pay attention too much to that piece. I actually thought it was broken or user-modified.

But, now I think it's a crank case drain plug socket. Snap-on had a similar piece, P-10, from their 1926 catalog.
http://www.collectingsnapon.com/catalogs/catalogs.php?loggedin=0&catalogPage=48

[OilyRascal]

I believe it was user abused, not modified.  It does not have a detent ball, and it does have original plating around the square sides of the 5/16" working end.

It seems the consensus is a plug/drain socket.  Clearly Snap-on had one the same (thanks Jim).  I appreciate the input and will research from there.

[Billman49]

In the UK 9/32 inch drive sockets were available - mainly ex MOD sets (BA sockets) - made to contract by firms such as Britool...

[scottg]

Conduit fittings have square holes.
  Like a pipe plug (which always has a male plug on the end),   a conduit plug is shorter and more compact for tight spaces, with a female drive.    Always galvanized as far as I have seen.
  yours Scott

[junkfisher]

this is straying a bit from the 5/16, but I had a set of impact sockets that were in the metal box even had a 4" extension. they were 5/8" drive. I kept running across them until I finally found room in the tool shed for them. I thought they were 3/4 drive when I tried using one on my 1/2" drive impact. months later I was using 3/4" drive breaker bar and grabbed them then I found out that they were 5/8" drive and I couldn't use them. sold the whole set at a flea market for $10.00 so I could save myself from grabbing them when I needed something I could actually use.