The ISC Small Aluminum Arborist Rigging Block (5/8" Rope) is designed to work to absorb the huge forces which are created by the harsh dynamics of heavy Arborist work. The compact design and the unique upper sheave opens and closes and secures easily. 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.