Single, Swivel Head, with Acetal Sheave and Ball Bearings The new Series 40 ball bearing Orbit Blocks™ provide the perfect balance of strength, performance, and reliability. They offer class-leading dynamic and static load ratings, the highest available in this size of performance blocks. Lightweight and strong toughened glass fibre reinforced nylon cheeks replace stainless steel straps used in traditional utility blocks - the perfect balance of performance and reliability. The RF48100 Single Block features a 40mm (1 9/16") sheave and incorporates our 2-stage bearing system. Ball bearings minimise friction while a secondary full-contact bearing maintains low friction across the full working load range. This product does not have a locking headpost, which is only available in the multiple sheave variants. RF48100 is free swivel rotation only. RF48100 is free swivel rotation only. This product does not have a locking headpost, which is only available in the multiple sheave variants. Applications: Mainsheet systems and spinnaker sheets on dinghies, off-the-beach catamarans and sportsboats to 8m (26ft). Halyard, vang, and backstay applications on boats to 8m (26ft). Control line applications on larger yachts. Materials: Sheave and Ball Bearings: High compression strength acetal. Frame/cheeks: Toughened, glass fibre reinforced nylon. Head fittings, hubs, and fixtures: Grade 316 stainless steel.