Spring Lock Aluminum Blocks from ISC.

? Blocks are made from high tech aluminum alloy so they are incredibly light, but strong.
? Aluminum alloy bushings and sheaves are supported by stainless steel axles and bronze bearings.
? Bushings are easily accessed by quick-twist nob, and are captive, so they can?t get lost.
? Cheek plates are broad enough to protect lines during use.
? Blocks are rated to 100 kN (working load limit of 4,800 lbs.) and weigh approximately 3.5 lbs.
? Sheave diameters are 2-3/4".