Ball nose mills

Indeed. The Clarkson Dedlock style collet is rather interesting. The tools screw into a collet, and then the collet and tool are put in the holder and the cap is tightened. The end of the cutter sits against a centre-point n the holder. Cutting torque then screws the cutter into the collet, but because the tool is hard against the end-stop the effect of this is to force the collet down into the end cap, gripping the tool.

It is semi-clever. The tools always sit at dead-length, and the harder you cut the tighter the grip. But if the thread on the tool is too short (and some are) you can end up with a tool that is loose in the chuck _and_ is irremovably tightened into the collet.