Replaces unsuitable terminals with non-parallel clamping surfaces or too small surfaces. These seat clamps are specially designed for Pitlock seatpost skewers. Pitlock locking skewers are designed to work on flat, parallel surfaces. If your bikes existing seat post does not have flat surfaces to accommodate the spit, you will need to replace the unsuitable clamp with a clamp specially designed by Pitlock Standard length (33mm) pitlock seatpost spike fits Pitlock seatpost clamp/collar. To replace your existing seat clamp, measure the outer diameter of your seat tube.