These new ball bearing blocks are extremely light and stronger. Use the 2 1/4" composite blocks for mainsheet systems on catamarans and for control lines, vangs, cunningham and spinnaker on little and medium sail-boats. Delrin ¤ sheave and ball bearings. Composite cheeks, stainless steel (AISI 316) rivets. All the blocks with shackle have universal 3-way head and may be fixed in two different positions or swivel freely.