Cold forged and CNC&';d from 6061-T6 aluminum alloy, the MX37 seatpost clamp is tough, lightweight and safe for use on carbon frames. 31.8mm diameter black with laser-etched graphics and stainless steel hardware 6061-T6 aluminum alloy Bolt-on design Stainless hardware Safe for use on carbon frames Material: Alloy Type: Bolt-On Diameter: 31.8 Color: Black