Ronstan Series 55 BB Orbit Block, Double Becket Swivel [RF55210]Series 55 BB Orbit Block, Double Becket Swivel Lightweight Kilogram for a kilogram of working load, BB and RT Orbit Blocks are the worlds lightest. 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