What is this size??

[Millerfish]

This wrench is marked 3/8 SAE, It measures .575 across flats. That doesn't seem to match anything...

 

[Oldtuleguy]

3/8 bolt diameter

 

[cody1325]

Recently had this confusion with an old Williams wrench I had. Apparently, these are not measured across the flats compared to modern SAE. I think they changed it sometime in the '20s. That being said, virtually all my really old Williams stuff is larger than what's stamped on the wrench (though one has SAE, USS, and British Standard all stamped on it).

 

[kaymccampbell]

It's 9/16. Which is typically the head size of a 3/8 bolt.

 

[Provincial]

A 3/8" SAE fastener has a 9/16" hex head. 9/16" = .5625" and given a little latitude for slipping the wrench onto the fastener, the extra .012" qualifies for 9/16 wrench.

 

[mikegt4]

Back in the day wrenches often used to be marked with the bolt (thread or shank) size. IIRC, war production standardization efforts firmed up hardware standards.

 

[Millerfish]

This wrench is marked 3/8 SAE, It measures .575 across flats. That doesn't seem to match anything...

How did not see it 9/16" Doh!

 

[Provincial]

How did not see it 9/16" Doh!

You were looking at the .0125" difference. It throws you off!

Actually, it is hard to remember that the wrench opening needs to be a little large to facilitate getting it on the fastener easily.