The FSA Compressor ACR aluminium expander set it is suited for 1 1/8 inch steerer. It is installed instead of the ahead star nut and prevents damage to the steerer tube. The use of a compressor is recommended for carbon steerer tubes.

Aero Cable Routing System

ACR System, a fully integrated Aerodynamic Cable Routing solution that routes all cables, wires and hoses internally, is available for FSA and VISION's top-of-the-line handlebars. This innovative patent-pending system is unique to FSA and VISION, and is a combination of thier knowledge bases in both headset and cockpit development and manufacturing, plus the FSA/Vision history in aerodynamic development and design. The result is a clean, integrated and aerodynamic cable routing solution for frame and bicycle brands.
The CORE of the ACR system is built around the handlebar, headset and stem that easily allows brands a "plug-in" solution for clean and simple cable routing for their frames. By using standard headset dimensions, the system maintains frame strength and, by routing cables through the headset, it also safely preserves a round steering column.
Material: aluminium
Weight supplement: manufacturer information