Check the listing for details. Porkchop BMX 21.1mm quill chromoly CR-MO threadless stem adapter for 1" threaded. Condition: New. Listed at 29.99 USD. Porkchop BMX quill stem threadless stem adapter - made of chromoly steel. This adapters allows you to run a 1 1/8" threadless stem on your old school BMX bicycle (with 1" threaded fork that uses a 21.1mm quill stem) * Color: CHROME * Material: 4130 chromoly steel * Length: Overall 171mm - maximum rise from minimum insertion mark to top of stem mounting is 88mm. * Stem requirements: Uses a 1 1/8" threadless stem not thicker than 40mm where it attaches. * Quill size: 21.1mm (this is common for 1980's BMX bicycles, however a very similar common stem size is 22.2mm which this will not work for. You must carefully measure the inside diameter of your fork steer tube to be sure which size stem quill your fork requires) * Includes hollow Potts Mod bolt to allow for brake cables to be run inside of fork steer tube if desired.