QUILL VS THREADLESS

Every stem question on a track bike comes back to one thing: is the steerer tube threaded? Everything else follows from the answer.

Quill: inside the steerer

A quill stem drops into the steerer tube. A long bolt runs down the middle and pulls up a wedge (or a cone) at the bottom, which jams against the inside wall of the steerer and locks the stem in place. On a 1 inch steerer the quill itself is 22.2mm.

This only works on a threaded steerer, because the threads are what the headset locknut clamps onto to hold the fork in the frame. The stem and the headset are doing two separate jobs.

Threadless: around the steerer

A threadless stem clamps around the outside of the steerer. There are no threads anywhere; a top cap and a star nut (or expander plug) pull the fork up to set headset bearing preload, and then the stem's pinch bolts hold everything in position.

Here the stem is structural to the headset adjustment. Loosen the stem and the bearing preload goes with it.

They do not swap

A quill stem cannot go on a threadless steerer — there are no threads for the headset, and the wedge has nothing sensible to bite. A threadless stem cannot go on a threaded steerer in the ordinary way either. Our compatibility engine returns these as hard incompatibilities rather than "maybe":

1 inch threaded · 1 inch threadless · 1-1/8 inch threadless

Height adjustment is the real difference in use

Quill adjusts by sliding up and down inside the steerer. You get a continuous range, bounded at the top by the minimum insertion mark — which is a structural limit, not a suggestion. Raising the bars is a two-minute job with one bolt.

Threadless adjusts by moving spacers above and below the stem, and by flipping the stem over. Your ceiling is however much steerer is left above the headset. Once that steerer is cut, it is cut — which is why anyone building a track bike should ride it before trimming the fork.

Converters

A quill-to-threadless converter is a quill stem whose top end is a threadless clamp. It gives a threaded fork a length of exposed 1-1/8 inch tube, so you can run modern threadless stems. It solves a parts availability problem, not a structural one: the load still passes through a wedge inside the steerer, and the stack height goes up.

Going the other way — running a quill on a threadless fork — has no equivalent, because the missing threads are missing.

What this means when you are shopping

Work out what your fork is first, then filter. On this site the standard page carries the list: every stem we hold data for that fits a 1 inch threaded steerer is generated from the database, not typed out by hand.