Avian Compression Top Cap (expander Plug)Avian compression caps to fit 1 1 8 size headsets, The Expander Plug included with our 1 1 8" Standard & Tapered headsets is intended for use with 1 1 8" fork steerer tubes with a 23. 2 Inner Diameter. That means if your fork has a steerer tube thicker than 2. 7mm, our expander plug won't fit inside it. Fork manufacturers that use thicker steerer tubes than 2. 7mm should require a stem lock design, or some other type of internal locking included with