The VO threadless stem adapter allows you to use threadless stems on a bike designed for a quill stem. The advantages include the ability to use nowadays commonly available threadless stems with a variety of rise angles. Many threadless stems also have removable face plates, so bars need not be "stripped down" when switching bars or stems. Threadless stems can be "flipped" for additional rise or drop.
Genetic Stem Adapter. The VO adapter is popular and often goes out of stock. We have found an almost identical alternative for when the VO is out. 50mm clamping area and 190mm long.