Harken 38mm Big Bullet Single Block includes an integral becket that allows either a 2:1 or 3:1 purchase. 

Big Bullet blocks can be used as main or jib sheet blocks on dinghies, or for control line applications, such as travelers, cunninghams or boom vangs on offshore boats. Low-friction Big Bullet Blocks lead control lines aft. They are compact and lightweight, with fast trim and release under high or low loads. Delrin sheave and ball bearings. Cheek material constructed from reinforced plastic with stainless steel straps. Where applicable, blocks use #10 fasteners.

• Use as main or jib sheet blocks on dinghies, or control lines on offshore boats
• Delrin® ball bearings
• Wrap-around stainless straps
• Lead control lines aft
• Hardkote-anodized Teflon impregnated aluminum sheaves
• Sheave Diameter: 1 1/2" (38 mm)
• Max. Line Diameter: 3/8" (10 mm)
• Max. Working Load (MWL): 300 lb. (136 kg)
• Breaking Load: 2000 lb. (907 kg)
• Weight: 2 oz (57 g)
• Length: 3 1/2" (89 mm)