I made a generalization of the ubiquitous 5C collet blocks. The picture below shows it in its assembled state.
Shown below are the two main components of the device. On the right is the collet chuck which is shaped exactly as one would shape a 5C chuck internally. On the left is the clamp that holds the chuck. It is split and fitted with a SHCS to lock the chuck in place when required. (When the clamp is used in the mill vise the clamping action of the vise closes the clamp and the screw is not required.) The clamp is fitted with a small brass finger stop that allows it to be accurately re-positioned in the mill vise.
The chuck has a dead flat bottom so it will sit vertically in the mill vise. When this flat base is aligned with the clamp base, the 24 indexing holes are just above the top of the clamp and precision pins in the chuck can be used against a pin fixed in the clamp to effect the indexing action.
These pictures show the draw-nut used to tighten the collet and the spanner used to tighten the draw-nut. When the nut is fully tightened on the collet in use it's completely hidden up inside the recess turned in the base of the chuck. This is done so the chuck can sit flat when used vertically.
Since the draw-nut is hidden when tightened, a special spanner is needed to reach up into the recess to tighten/loosen the nut. The one shown will do that. It has holes for tommy bars to provide the torque to activate the nut.
This strange cylindrical spanner shape accommodates the situation where the collet is used horizontally on a long piece of stock that projects out of the back of the collet. The spanner is slipped over the projecting stock, its "teeth" engage the slots in the nut, and the tommy bars activate the nut.
This is one of my most useful tools. You'll never believe how many small dividing jobs can be done with it.
I occasionally need to mount a small part on a faceplate so I made a tiny one to fit into a 1" collet.
The T-slots were made with a 1/4" mill reground to look like a T-slot cutter. The T-nuts are 6-32. The back view,
shows the spigot used to mount it in the collet. The spigot is removable
and has a precision centering pin so that other fixtures can be fitted to it. (A sacrificial mounting plate is shown on the right.)
Finally, with the spigot removed, the faceplate fits into my vertical collet holder to form an indexing table. The bushing shown fits into the table's central hole to reduce its diameter if working on parts smaller than 1/2" OD.