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. Spring lock bushings are easily accessed by a quick-twist nob, and are captive, so you won’t loose it. Sheave is supported by a sintered bronze bushing. Cheek plates are broad enough to protect lines during use and painted with a tough, powder coated finish. Individually inspected and CE approved.