Differential pulley the system becomes a simple "gun tackle" with a mechanical advantage of 2. The same principle is used in a differential windlass, where the connected pulleys are replaced by winches. In the above graphic, the four segments of the chain are labelled W, X, Y and Z. The magnitudes of their corresponding forces are "F", "F", "F" and "F", respectively. Assuming that the chain is massless, "F" = 0 because segment X is not supporting any weight. Taking the system at equilibrium, "F" and "F" are equal — if they were not, the lower pulley would freely turn until they
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