cable. For example, head blocks are typically used with GAC, but blocks may be used to facilitate flying heavier line sets (e.g., electrics). Mule block Lift lines sometimes require diversion to avoid obstacles, support non-linear loads and battens, deal with excessive fleet angles, or be reoriented from the typical transverse path across the stage (e.g., for tab and light ladder line sets). Mule blocks are single or multi-line blocks able to divert the path of those lines. Mule blocks may be permanently installed as part of counterweight rigging systems, or used for spot rigging, where they are often equipped with swivel-pivots to divert lines across a large range of angles. Tension block 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 Counterweights are heavy objects that are used to balance the lineset loads in a fly system. In hemp systems, a counterweight consists of one or more sandbags, whereas counterweight systems employ metal bricks as counterweights. The term counterweight is commonly used to refer specifically to the metal counterweight bricks. Metal counterweights are lead, cast iron, or flame-cut steel. Flame cut steel bricks are most common. In any particular fly system all counterweights typically share a common, standardized footprint that matches the system's arbors, which in turn are sized to conform to line set spacing. Counterweight systems are most often designed to use either 4 or wide weights. Weights vary in thickness, typically in half-inch increments ranging from 1/2 to , with each thickness corresponding to a different mass. thick weights are most common. Counterweights are sometimes also known as bricks or simply steel. Often a rigging worker will be asked to load a number of inches of steel, which correlates to a specific mass. Weights are usually loaded from the loading bridge, but can also be loaded from the fly gallery or stage deck in some circumstances. When viewed from the top, metal counterweight is basically rectangular, typically with 45-degree angle chamfers cut at two opposing corners. A slot is cut into each end of the weight so as to enable the weight to