I bought this same set yesterday without knowing! Can't believe it. Just when I thought my life couldn't get any weirder.
Grabbed it at an estate sale but never looked at the sockets, assuming they were Bonney like the flex extension. Two Williams sockets were in there too.
I have to agree with you guys, they look S-Kish to me. They have the flat bottoms like old SK sockets for one thing. Duro/Indestro is a good guess too because of all their unmarked tools. I think Bonney marked all their tools. One thing I know for sure, they aren't Williams.