d.

I've seen in the MSC flyers from time to time a tool which has
three flanges on a handle, to allow you to hold the collet from rotating
more easily (without a tool in it), or to allow you to unscrew the
collet from the spindle (without an index pin being there). The flanges
fit into the three radial slots on the collet's end, to allow you to
either rotate it or to stabilize it.

I think that this tool is intended to be used on CNC machines
where the collet is tightened by power assist.

Collet wrenches are used on collet closers to install/remove the collet. --Doozer