Is 1/2" really 13mm?
 

Are they really interchangeable or are the fasteners we use just not precision machined?

What I'm really wondering is if a 1/2" and 13mm from Craftsman is really the same wrench/socket.

1 inch = 25.4mm

1/2 inch = 12.7mm which means a 13mm wrench is just a bit wider than a 1/2 inch wrench. They may not the same, depending on manufacturing toleranced, but close to work on many fasteners.

The fasteners themselves are NOT interchangeable, as the thread pitch is not equal, and will ruin the fastener or the tapped hole.

I investigated a case where an oil filter fell off of a car, ruining the engine. The filter had a SAE thread, the engine wanted a metric thread. The SAE was just slightly larger, allowing the filter to fall off 5 miles after it had been installed. Filters looked exactly the same, except for part number...


Best Regards,
Jim

I'm certain that they are not the same.

The 13 mm is nominally .512".

The manufacturing tolerances for the sockets are probably in the order of .005 total.

Someone with a pair of mics please go measure already. :)

Is a 13mm wrench actually 13mm?
No. It has to fit on a 13mm fastener, so the wrench size is going to be a bit larger than "advertised."

Using new S-K combination wrench, here is what I measured:
1/2" = .505"
13mm = .514"

With Craftsman wrench (Used) I get:
1/2" = .505"
13mm = .517"

I often substitute a 13mm wrench for a half inch wrench, and visa-versa. I find that while a 1/2" wrench will fit a 13mm bolt head, it usually fits very loosly, and the 13mm wrench over a 1/2" bolt head will be a bit tight, but still works effectively! .............BB

I suppose I need to get my caliper calibrated.

I regularly interchange 5/16 and 8mm,,,, 1/2 and 13mm, and 3/4 and 19mm. They are all close enough for government work. ;)

A set of 6-point metric sockets will cover just about all your SAE needs. It doesn't work so well the other way (using SAE on metric) because the difference in size between each SAE is more than 1 mm. But 6-point is the key!

Jeff Pierce