collet

noun3

1. •
   A band, flange, ferrule, or collar, designed to grip and hold a tool or a workpiece under proper control, and usually to release it under control thereafter; such a collet usually is made of a hard, springy material, especially a metal.

   • That collet can handle up to 3/8-inch bits.
2. •
   The rim (of a ring) within which a jewel is set.

   • There is an almost invisible collet that secures the stone to the ring.
3. •
   In an embryonic plant, the transition zone between the root and the hypocotyl (not clearly distinguishable in most plants.)

   • Collar rot forms in the collet between the stem and the root.