Sheaves are wide enough to pass two 7/16" sheets. They pivot 40 to accommodate changing sheeting angles. The Small Boat and Mid-Range blocks feature ball-bearing sheaves and ride on traveler car bodies with Torlon bearings. They accommodate appropriately sized traveler control line blocks to create additional purchase. The High Performance car features a roller/ball bearing sheave for higher working loads, and rides on low friction sliders. It has a lever-operated pin stop that operates easily even with cold hands, and can be locked open and used to dead-end an adjustment line. Note: These blocks fit Harken low-profile traveler track Configuration: Twin sheet lead block Sheave: Anodized aluminum Ball Bearings: 249, 1537 - Torlon ball bearings, 1997E -Torlon roller/ball bearings Sheave Size: 2 1/2" (64mm) Line Dia.: 1/2" max. Cheek Material/Finish: 249, 1537 - Polished stainless; 1997E - anodized aluminum Shackle/Strap Type: Pivoting sheave carrier with control block or pin stop