The Uncle Mikes extensions do have micro allen set screws, usually two of them and they originally came with a blue thread lock on them. IOW, one was tightened against the hammer, the other against the first screw so it would not looosen - the idea being not having to over tighten them. Ever meet a Contender Maniac that wasn't a 900 pound gorilla? So the blue lock compound makes them hard to remove without stripping. The allens are either .035" or .050" I think (less likely by maybe .060"), not something you're going to buy at your local Lowe's, Home Depot, etc. I'd still have an extra one to measure if I knew where my old Contender tool kits was now, probably out in storage someplace since I sold off all my Contenders.
I sold/gave 2 or 3 of the UM sets with wrenches to folks here on GBO about 1-2 years ago - don't remember to who for sure though. Maybe one to Walt (Hopalong) as i gave him some of my other TC parts.
There have been other brands. Custom shops have also made their own versions. The UM sets are pretty distinctive though, easy to recognize.
Here's a pic of UM barrel bands and extensions I found still on my computer from when I sold them that may help...
