Collet Types: 5C, 16C, TF20, and What Fits What

By Bradley Taylor · August 2026

Walk up to a lathe you have never run before and the first practical question is what collets it takes. The answer decides what tooling you can borrow, what you have to buy, and how big a bar fits through the spindle. This is a tour of the common types, what each one is good at, and the one concept, dead length, that trips up almost everyone the first time they run a Swiss subspindle.

Why collets instead of a chuck

For bar work a collet beats a three jaw chuck at nearly everything. A chuck grips on three lines of contact and a collet grips almost all the way around the bar, so the holding force is spread out instead of concentrated. That means you can grip harder without marking the part, which matters a great deal when the surface you are gripping is a finished diameter. Collets are also fast. Open, feed the bar, close, and you are cutting again in a couple of seconds, which is the whole reason bar fed machines exist. And they repeat. Put a bar in a clean collet ten times and it lands in nearly the same place ten times. The tradeoff is that each collet only covers a narrow band of size, a few thousandths around its nominal, so you end up owning a drawer full of them instead of one chuck. For production work on round stock that trade is not close.

5C, the default answer

If someone in an American shop says collet with no other context, they usually mean 5C. It is the universal standard for small work. Capacity runs to about 1 1/16 inch in round stock, with hex and square available in the smaller sizes. What makes 5C valuable is not really the collet, it is the ecosystem around it. Manual lathes, collet chucks on CNC lathes, spin fixtures for grinding, indexers, collet blocks for the mill vise. Buy a set of 5C collets once and they follow you all over the shop. The 5C body also carries both internal and external threads. The external thread on the back is what the drawbar or closer grabs. The internal thread up front takes accessories, most commonly a work stop so every part locates at the same depth, and expanding arbors that hold a part on its bore instead of its outside diameter.

16C and the rest of the family

16C is what you find on a lot of CNC turning centers. It takes round stock to about 1 5/8 inch, and the collet is shorter and stouter in proportion, which suits the cutting loads a modern turning center can put into a bar. If the machine has a 16C nose and your work is all under an inch, it still runs fine, you just buy 16C collets instead of reaching into the 5C drawer, and you grumble about it exactly once. There are other members of the family. 3J sits between the two in capacity and 20C goes larger still, and you will meet both eventually, but 5C and 16C cover the great majority of what is out there.

TF collets and the Swiss side of the shop

Swiss lathes and gang tool machines mostly run TF style collets. TF20, TF25, and TF37 are the common sizes, and the number tracks the bar capacity of the spindle it fits. On a Swiss machine the main spindle collet lives behind the guide bushing and the subspindle carries its own collet, and the subspindle is where the interesting requirement shows up.

What dead length actually means

An ordinary draw in collet, like a 5C in a manual lathe, closes by being pulled backward into a taper. As the taper squeezes the collet shut, the collet and everything in it move back a small amount, typically a few thousandths. For most work nobody ever notices. Now think about what a Swiss subspindle does. It reaches out, grips the finished end of a part that is still attached to the bar, the cutoff tool parts it free, and the sub carries it away and faces the back to length. If the collet drags the part backward as it closes, your overall length moves by that amount, and it moves by a different amount depending on how hard the collet happens to close on that diameter. A dead length setup avoids the whole problem. The closing mechanism moves around the collet instead of pulling the collet through a taper, so the part stays put in Z while the grip comes on. That is why pick off work and dead length closers go together. When the length of the part depends on where the collet left it, you want a collet that does not move it.

Emergency collets

An emergency collet comes soft, with a small pilot bore, and you machine it to fit the job. Bore it in place in the spindle and the gripping surface ends up true to that spindle, which is the whole appeal. They are the answer for odd diameters no standard collet covers, for stepped bores that grip a part against a shoulder, and for holding a finished part by some delicate feature a standard collet would mark. Bore them with the collet closed on a pin or with the leaves held at working position, following whatever method the maker recommends. Boring one wide open and hoping is how you make a collet that grips on three corners.

Care, and what runout to expect

A collet system is only as good as its tapers. One chip caught between the collet and the spindle bore prints itself into every part as runout, and it does it so consistently that you will chase it in the program for an hour before you think to pull the collet and look. Wipe the collet taper and the spindle bore every time you swap, keep a light film of oil on the taper, and store collets somewhere chips do not rain on them. And never crank a collet closed on nothing. Slamming one shut with no bar inside springs the leaves past where they were meant to go, and a sprung collet never grips quite right again. As for accuracy, a clean 5C in decent shape typically runs somewhere from a few tenths to about a thousandth at the collet face, and good ground collets in a good spindle can do better. Treat those as typical numbers, not promises. Condition, cleanliness, and how close the bar is to the collet's nominal size all move the result.

The short version

5C for small work and anything that has to travel between machines and fixtures. 16C for bigger bar and a stiffer grip on a turning center. 3J and 20C when the machine says so. TF sizes on the Swiss side, with dead length closing on the subspindle whenever you pick off and face to length. Emergency collets for everything the catalog does not cover. And clean tapers everywhere, because the finest collet ever ground cannot grip around a chip.

As always, this is general practice, not a spec. Prints, customer requirements, and the machine builder's documentation win every argument.