The rope-friendly edges, large sheave, and retained upper sheave which opens quickly with the twist and push pin are the same as the popular small ISC block, but with beefed up strength. Eliminates the chance of dropping a sheave. The lightweight and strong sides are now made with Hot Forged Technology. The side plates are thick aluminum with a powder coating to enhance the life of the block. These blocks are rope friendly, durable and extremely robust.