Series 70 BB Ball Bearing & RT Ratchet Orbit BlocksThe Orbit Blocks are designed to handle lines up to 1/2" diameter. Ideal for sheet applications on keelboats up to 30' and control lines on larger boats. Sheave: Carbon reinforced, PTFE impregnated engineered nylonBall Bearings: Series 70 BB Ball Bearing & RT Ratchet Orbit BlocksSheave Size: 2-3/4" (70mm)Line Dia.: 1/2" (12mm)Cheek Material/Finish: Glass-reinforced nylon