Ronstan Series 55 BB Orbit Block Double Becket Swivel. The unique orbital design allows the bearing to only be in the active areas of the floating sheave. This minimizes the mass of the inactive return race and hub.Weight and bulk are further reduced in the different block configurations. The ball bearing single and becket block have a through-sheave becket arrangement. The result? The lowest weight is possible.Multi-sheave blocks have only single intermediate cheeks and an ultra-light and efficient head arrangement. This gives a 30percent weight-saving advantage over the nearest competitor. Other brands just link together their single blocks. This results in unnecessary double cheeks between each sheave held together by a heavy steel channel across the top of the block. Specifications for Ronstan Series 55 BB Orbit Block: Manufacturer: Ronstan Color: Black Package Contents: Ronstan Series 55 BB Orbit Block Ronstan RF55210: Series 55 BB Orbit Block Double Becket Swivel