A collet is a metal insert for a machine's chuck. When tightened, the collet compresses around the work piece, holding it firmly in place for machining. A number of collet standards are made to fit different chucks. If your machine calls for a 5c collet, no other size will fit. Certain specifications apply to the 5c collet standard.
Length
A 5c collet measures exactly 3.27 inches from end to end. This measurement does not necessarily dictate the length of a part that can be machined with it. A part that does not require a stop for accurate machining to length can hang out the back of the collet. An extender tube can be screwed onto the inner threads of the collet, providing extra length for a part that requires a stop.
Back Bearing
A 5c collet back bearing must measure 2 inches from the top of the threads to the beginning of the taper. It also has a 1.250-inch outer diameter. A notch has been cut into this section of the collet. This notch aligns with a pin on the spindle of a machine to ensure the collet is inserted properly.
Taper
The outward taper of a 5c collet measures 10 degrees. It is an angled part that protrudes from the body of the collet. The angle has to measure perfectly in order to fit properly in the angled chuck of a machine.
External Threads
The external threads for this collet standard must be 1.238--20. This designation means that the threads have a 1.238-inch outer diameter and contain 20 threads per inch. The threads are right-handed, which is standard.
Capacities
A 5c collet has a limit on the size of part it can hold properly. Rated maximums apply to each of the opening shapes. Round openings have a maximum diameter of 1 1/16 inches. Hexagonal openings have a maximum diameter of 29/32 inch. Square openings have a maximum size of 3/4 inch.
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