Collet
Affiliate link — we may earn a commissionA collet is a slotted sleeve that grips a tool shank by compressing around it when a nut is tightened. Routers use collets to hold bits (1/4-inch and 1/2-inch are standard). Impact drivers use a spring-loaded 1/4-inch hex collet that locks and releases with a pull-ring. Die grinders and rotary tools use collets from 1/8-inch to 1/4-inch. Unlike a drill chuck, which clamps with three jaws, a collet grips the entire circumference of the shank, which gives better concentricity (less wobble) at high RPM. The trade-off is that a collet only accepts one shank size per sleeve.
Why It Matters
On a router spinning at 20,000+ RPM, any wobble from the bit holder translates to a rough cut and premature bearing wear. The collet's full-circumference grip keeps the bit running true. Use the right collet for the bit shank. A 1/4-inch bit in a 1/2-inch collet with a reducer sleeve works but adds runout.