The seatpost clamp should match the diameter of the seat tube on your frame and not the diameter of the seatpost itself. The M5 bolt includes spherical washer and mates with a cylindrical anchor barrel. This means that threads are always perfectly aligned, preventing binding and ensuring consistent clamping force. Lightweight 6061 T6 aluminum, M5 stainless steel bolt with integrated washer Tool interface: 4mm hex key CNC Machined in Minneapolis, MN The precision-engineered Wolf Tooth Seatpost Clamp secures your seatpost and looks good doing it. At the heart of the Wolf Tooth Seatpost Clamp are our custom self-aligning bolt and anchor. The M5 bolt includes spherical washer and mates with a cylindrical anchor barrel. This means that threads are always perfectly aligned, preventing binding and ensuring consistent clamping force.