Replaces your existing 1 1/8" stem cap. You can mount one of 7 included computer heads, or a GoPro - May not work with large computers and hi-rise stems, check clearance before ordering - Included in package: BF4 aluminum stem cap with stem bolt and hardware, BF4 4mm spacer (to raise mount if needed), 7 Computer heads (Garmin, Polar, Wahoo, Mio, Joule, Cateye, Bryton, GoPro/Finned mount) - 35.0 and 31.8mm diameter handlebar clamp compatible (hardware included)