Interesting points. When I was a Snap-On dealer many years (1978-85) ago I was told that all of their hand iron was made from chrome-moly steel, which I tend to believe. As a tool dealer I saw many broken sockets (and many injuries) from many different brands. I would refer to chrome-vanadium tools as “glass” tools due to the way they broke. Most of the time, when a Snap-On tool broke, it would simply crack along a line, but remain intact. CV tools would frequently fracture into multiple pieces, which made them shrapnel generators when used on impact tools. How the tool was heat treated also made a great difference. There used to be a great film from Snap-On that showed how their combination wrenches were heat-treated differently on open and box ends. It showed workers flipping the wrenches over in tubs of salt so they could be put back in the heat-treat ovens to treat the opposite end to a different spec.
A couple of other points. Chroming steel can cause a problem called hydrogen embrittlement which also can cause fracturing in steel if not dealt with properly. I suspect some of the cheap, “shiny chrome” tools I’ve seen over the years suffer from this problem. One more thing - look closely at the pictures of the socket ends in this article. You’ll notice that the corners of the sockets are radiused and are not sharp angles. Snap-On used to hold the patent on this broaching process, and it was called flank drive. When the patent expired, most tool makers copied it for their sockets, wrenches, etc. I owned a jet boat for many years that I named “Flank Drive.” I had a traveling artist paint it on the stern with the end of a socket showing the corner radii and the Snap-On logo in red. It’s still plying the waters of Lake Havasu, albeit with a new owner.
