These new ball bearing blocks are extremely light and stronger. Use the 1 1/2 " composite blocks for jib and mainsheet systems on dinghies and small keelboats. Delrin® sheave and ball bearings. Composite cheeks, stainless steel (AISI 316) rivets. All the double and triple blocks with shackle have universal 3-way head and may be fixed in two different positions or swivel freely.