Schaefer blocks rely on a variety of sheave designs, materials and scorings. Derlin - Sheaves are injected molded with UV inhibitors and monitored molding cycles leading to a strong, UV resistant product. These sheaves offer durable, lasting service for all applications. Aluminum - This configuration accommodates both line and wire, providing a chafe-free surface for line while giving full support to wire to prevent flattening. Made with 6061-T6 Aluminum.