Inspired by some video's I saw on you tube, I just had to have one.
Take a 3/4" stub of 1-1/4 steel round and machine down the threaded area to 1.041. Then single point thread it for 24 tpi) This will then screw into the back of a C5 collet. The center of this gets drilled and tapped for 3/8-24 bolt. A flat area is milled on 2 sides so a 7/8" wrench will fit.
The 3/8 stop bolt I made from a piece of 1/2" steel round. (the un-turned section goes inside the collet and will be the stop) A 3/8-24 nut finishes it off so you can lock in your setting.
A nice item for making repetitive parts. (a great project to practice your threading too) lol