General: Quickie

There is no way you can add a threadless stem to a threaded frame, right?

Frames aren't threaded for stems.

So if I bought a bike with a threaded fork/frame, I could convert it to a threadless?

Greg, can you explain how that converter works. I can't figure it out by looking at it!

Okay, let's begin at the beginning, without snarking at the newbie.

First, check the Writ of Common Wisdom, the late great Sheldon Brown. He's an excellent choice for explaining all the terminology, and he does it in a way that doesn't mock people who don't already know this stuff. His key points for this issue are contained under headsets and stems.

There are four components in this discussion: The frame, the fork, the stem, and the so-far-unmentioned headset. The headset is the part that holds the fork in the frame. It's the assembly that fits at either end of the head tube (the tube at the front of the frame through which the fork's steerer tube goes).

The threaded/threadless distinction comes from the headset and the fork, not from the stem. A threaded headset holds the fork in place by screwing a nut onto the end of the fork's steerer tube. Because the nut needs to screw down on the steerer tube until it's snug against the top bearing of the headset (pressed into the head tube), the steerer tube has to be pretty short - usually less than an inch longer than the head tube. A threaded stem is an L-shaped component: One side of the L fits through the top part of the headset and into the steerer tube, and the other side projects forward to grip the handlebars.

In a threadless assembly, the headset doesn't clamp to the fork at the steerer tube. Instead, the steerer tube goes completely through the headset (forming the vertical side of the L in a threaded stem), and is clamped in place by the threadless stem (forming the horizontal side of the threaded stem L).

There are two ways to convert a threaded assembly to a threadless one.

The first costs a lot of money, and involves replacing everything but the frame and the handlebars.
1) Remove the fork and headset
2) Replace the threaded headset with a threadless headset of the same size
(1 inch or 1 1/8 inch, usually)
3) Get a for with a longer steerer tube
(the threaded fork has already been cut short to line up with the threaded headset, so you're going to need more height to clamp the threadless stem)
4) Cut the steerer tube of the new fork to an appropriate length
5) Fit the threadless headset, using spacers between the headset and the stem to get the height correct
6) Clamp the handlebars to the threadless stem

The second way is kind of rinky-tink, but it's faster and cheaper. You still replace the threaded stem, but this time you separate it into two parts. The horizontal part of the threaded stem is replaced by a threadless stem, and the vertical part is replaced by the threaded/threadless adapter, which clamps into the threaded headset/steerer tube assembly. Once the adapter is clamped in, you clamp the threadless headset onto the vertical extension of the adapter, as if it was a longer threadless steerer tube.

Most threaded/threadless stem adapters go from a 1 inch threaded part to a 1 1/8 inch threadless part, because most older frames are sized for 1 inch "threaded" forks/steerer tubes, while most newer "threadless" stems are sized for 1 1/8 inch steerer tubes.

Generally, it's technically inelegant to daisy-chain a lot of adapters. Think of a grounded appliance cable plugged into a grounded power strip, plugged into one of those red 2-prong/3-prong adapters, plugged into a 2-prong non-grounded outlet; the device may eventually fail, because it's not really plugged into a grounded outlet for which it's designed. In addition, every component (and every connection between components) introduces another point where something can fail.

Most threaded assemblies use 1 inch headsets/fork steerer tubes. This was the common size for almost all road and mountain bikes until the late '90s, and some custom road builders still use it. It is possible to get a threadless 1 inch fork (which makes the expensive version possible), but you don't get a wide choice in inexpensive forks.

Most threadless assemblies use 1 1/8 inch headsets/fork steerer tubes. Most newer bikes (except some road/track stuff) uses this size. Because it's the most commonly used size/format, it has a wide range of options at all price points.

The bigger metaphysical question is: What kind of bike do you want? Do you have a threaded arrangement that you're trying to convert to threadless, and what do you hope to gain by doing so?

Check my profile. There is one on my Trek 1420 light tourer. It is called a "quill adapter". Basically the quill part of a stem without the stem; you can clamp a threadless stem onto it.

There are pros and cons. A quill stem is more adjustable in height. However, threadless stems usually use a clamp that can be unbolted, allowing easy bar changes. Of course, one doesn't do that very often, so I'd say the one other reason is so you can convert to 31.8mm oversize bars (since a lot of quill stems are made for 26.0 or 26.4mm bars).

In my case, the 1420 came with an extremely deep-drop Modolo anatomic bar, which was uncomfortable. My spare set of Ritchey Pro bars wouldn't fit the 3T stem (25.4mm clamp diameter vs. 26.0mm bars). I ended up using a spare Bontrager Select stem lying around, so I didn't have to pay more for a stem, and quill adapters are cheap ($10-15).

there is, its a converter. it goes in just like a threaded stem. but you can put a threadless stem on it. they go for under 30$