FSA compressor sl expander plug with cap The FSA compressor plug is used to tie together your carbon steer tube fork, headset, and stem. The compressor plug expands as you tighten it inside the forks steer tube creating a safe and secure fit. This is the solution for forks with carbon steer tubes since you never want to use traditional star nuts on carbon. Features Safe for use on carbon steer tubes Includes carbon cap Lightweight design | Fsa | Compressor Sl Expander Plug With Cap | Black | 1-1/8", Alloy, For Carbon Steerer