Specifications include, but are not limited to: Head Blocks A. Type: single purchase twelve inch (12”) head block. B. The sheave shall be filled nylon, with a 12 inch outer diameter. The sheave shall be equipped with a one inch (1”) diameter shaft and two tapered roller bearings. C. Base angles shall be a minimum two inch (2”) by 1.5 inch by 1/4 inch angle with the short leg turned in and notched to allow clear passage of all cables. D. Side plates shall be a minimum of ten-gauge steel, and shall fully enclose the sheave. Side plates shall be bolted and welded to the base angles for extra strength. E. Mounting clips shall be steel, 3/8 inch thick minimum with a welded toe at least as thick as the mounting steel and punched with two oval holes for 1/2 inch bolts, flat washers and lock nuts. F. The block and associated mounting hardware shall have a recommended working load of at least 3,000 pounds. G. Head blocks shall be grooved for six (6) or eight (8) 1/4 inch lift lines and one (1) 3/4 inch hand line.