Bike Stem Guide

When purchasing a Carbon Bike Stem, you should consider several factors. First you must determine headset type (threadless or quill). Then you must match it to a steerer tube diameter and a handlebar diameter. Finally, you must decide what length and how much rise or drop you want your bike stem to give you. Once you have decided on those characteristics, you must decide on the material you'd like and consider its price.
Stem type
The two main types of bike stems are "threadless" and "quill." The type of stem required is determined by the headset and carbon forks installed on your bicycle--either threaded or threadless. Once you have determined which headset style your bicycle requires, you must determine the different compatibility factors: steerer tube diameter and handlebar diameter.
Steerer tube diameter
Carbon Bike Stem attach to the bike via the steerer tube. Threadless stems clamp around the steerer, while quill stems use compression to attach to the inside of the steerer.
* Threadless Threadless headsets and carbon forks come in four standard sizes: 1-inch, 1-1/8-inch, 1-1/4-inch and 1-1/2-inch. These sizes correspond to matching stem sizes. 1-1/8-inch headsets are the current leader in the headset race. However, with new trends always surfacing and old trends always resurging, this could change in the future.
* Quill Threaded headsets come in 1-inch, 1-1/8-inch and 1-1/4-inch sizes with corresponding quill stems sized down for the internal diameter of the fork's steerer tube. 1-inch threaded headsets were the industry standard for decades and remain very popular in the vintage and retro bike world. They remain the most widely used and readily available.
Handlebar diameter