I got these along with my mill, chucked them into a drawer and just found them a couple days ago. They look to me like types of boring head? Turning the indicator drives a worm that (presumably) moves the sleeve in and out, though the few with sleeves are very stuck. How is a tool held in these? There a cap head screw going through the bottom (one is sticking out in the picture) but it doesn't seem to do much.
I think these are a cartridge-style boring head. I think they take inserts similar to those shown here: https://www.zoro.co.uk/shop/microbo...ng/adjustable-cartridge-boring-system/f/26869 On some of the styles, the insert goes through the middle of the graduated dial, but on your ones, it appears to sit alongside the dial. As you say, the dial gives fine adjustment of the cutting bit. Perhaps the screw at the end is to lock it once set for proper diameter. They are for a fairly specific and narrow range of bore sizes, unlike a more general purpose boring head like a Nikken or Wohlhaupter.
Microbore inserts. They were mainly invented for semi production so they were set and left.I think they are a devlieg invention But they are really rigid which is useful, I use them on my newall jig borer but range is limited
Do we think these inserts are related? They are internally threaded, possibly for a tiny drawbar? Not that it matters now as I donated them all to a member on here.
You have seen more of these than I, but to me the ones he shows seem a bit unusual in that the bit appears to stick out at 90 degrees to the shank, meaning they cannot be used in blind bores, only through holes. On the Devlieg ones I have seen, it is always at 45 degrees, at the bottom of the tool.
