Here is a copy of what i found in 2013 post I wrote:
"Williams and Snap On are not the same. The steel and heat treats are different. Check the Snap On and the Williams on a Rockwell tester and report back with the results.
**Hint** The snappy is harder. Our Chief Metallurgist did some testing a few years ago and found there are big differences. I re-tested a handful of wrenches a few months back and re-confirmed the results.
Snap On: C-scale 55 (288,000 psi tensile/Brinell 560)
Williams: C-scale 50 (253,000 psi tensile/Brinell 481)"
Thread it came from:
http://www.garagejournal.com/forum/showthread.php?t=213584&highlight=williams&showall=1
Wrenches used:
15 or so old Williams Supercombos (made when full polish/chrome wasn't offered)
15 year old Snap On 4 angle wrenches
And my offer still stands with regards to testing sockets as I posted in the above thread.