Mechanical advantage assembly of a rope and pulleys that is used to lift loads. A number of pulleys are assembled together to form the blocks, one that is fixed and one that moves with the load. The rope is threaded through the pulleys to provide mechanical advantage that amplifies that force applied to the rope. In order to determine the mechanical advantage of a block and tackle system consider the simple case of a gun tackle, which has a single mounted, or fixed, pulley and a single movable pulley. The rope is threaded around the fixed block and falls down to the
Fly system used for spot rigging, where they are often equipped with swivel-pivots to divert lines across a large range of angles. Tension blocks are single-sheave blocks located at the lower end of the arbor guide track, beneath the arbor. The operating line is reeved through the tension block from the bottom of the arbor through the rope lock. Tension blocks typically ride vertically along the arbor guide system tracks, instead of being fixed, to allow for variation in the length of the operating line. Counterweights are heavy objects that are used to balance the lineset loads in a fly system. In