There is couple of options in fleabay too, the SLP 30102 which seems to be made out of old Craftsman sockets and then there is somebody who seems to make them by himself out of old sockets. Both these options seem a bit longer than the SO version though.
Interesting. I know some Craftsman deeps are full broach but I'd never paid attention to the plug sockets.
The Allen version looks like it's using 1/2" drive for porcelain clearance. Making that might be an easy angle grinder project for those of us who don't have machine tools.........................












