High-performance end controls allow the installation of 2:1 to 4:1 purchases. Designed for high-performance, free-running systems, Carbo control blocks with Delrin® ball bearings let cars instantly adjust and release under load. Assemblies secure to track, eliminating additional holes. Tough one-piece bases are machined from a single piece of aluminum. Delrin is a registered trademark of E. I. du Pont de Nemours and Company or its affiliates.