FSA Compressor plugs are proper complete top assemblies for carbon steerers to replace the traditional top cap/star nut assembly. Includes integrated cap, bolt, and expander.

The 1 1/8" size fits carbon steerer tubes with an inner diameter of 21mm to 26mm, and 1" fits most 1" threadless carbon forks.

If you have a 1 1/8" carbon fork and the inner diameter is smaller than 21mm, use the 1" version.