typically results in beams with a yield-strength significantly higher than the maximum loading condition, effectively providing a factor of safety. Fly loft The fly loft, fly tower or fly space, is the large volume above the stage into which line set battens are flown, along with whatever loads they may be carrying. In a full-size fly space, the tower height is ideally at least 2.5 times the height of the proscenium. This allows a full-height curtain or set piece to be located completely out of view of the audience without exceeding the travel distance of standard (single-purchase) counterweight arbors. Grid deck The grid deck, gridiron deck, or grid, is a permeable working surface present at the top of many fly lofts that is used to support and provide access to many of a rigging system's components. Though originally constructed of wood, down-facing three-inch steel channels with three-inch gaps became the prevalent grid decking in the 20th century. Today, large-opening heavy-duty steel bar grating is most common in new theatres. The grid deck surface is usually rated to support live loads as well as all anticipated dead-hung equipment and hemp and motorized (e.g., chain hoist) spot rigging. Its permeability facilitates the mounting of equipment and the passing of lift lines and electrical cables. Spot rigging is not feasible without a grid. The grid deck allows access to the "head block beam" and "loft block beams" of counterweight systems. Spanning from the proscenium wall to the upstage wall, these beams support the dead and live loads of a fly system. As per their names, counterweight system head blocks and loft blocks may be directly mounted to these beams. The head block beam is situated directly above the loading gallery. The loft block beams are spaced to match the "pick points" of the lift lines suspending the battens. The loft block beams may also be used to suspend the grid deck support structure. Rope line (hemp) head block well channels sit atop the grid deck and are used for mounting hemp system head blocks. They are situated above the pinrail(s) below. Loft block wells are ten inch gaps between pairs of face-to-face steel channels flush with the grid deck that occur beneath each loft block beam. The loft blocks of a hemp, or grid-mount counterweight, rigging system can mount to the loft block well channels. The loft block wells may also act as