The Tern Pinhead seatpost locks for GSD & HSD prevent the removal of your seatposts. Once installed, the seatpost locks remain permanently on your bicycle, even when you ride. When you need to adjust your saddle height, your Pinhead tool lets you do this quickly and easily with a 15mm wrench. Pinhead locks cannot be removed with tools such as hammers, pliers, picks, universal socket tools, grinders, or bolt cutters. Our convex disc technology prevents your parts from being removed by bike thieves.  Each key is different and comes engraved with a nine-digit code so it can be replaced if lost. With your key code matching, locks can be ordered to protect your other components or other bikes. All components are precision-forged from corrosion-resistant CrMo steel and aircraft aluminum alloys.