Figure 2-101.—Strap hangers from purlins.

Figure 2-99.—Completed S-and-drive connection. Figure 2-100.—Duct running parallel to purlins or beams. sufficient. However, if the duct is of a very large size, all edges, as illustrated in the figure which shows that a larger angle may be required. the duct system hanging from angle rails and that all The straps that are used as hangers may be angles be either bolted or tack-welded to purlins or fabricated from 1/8-inch plate. In a normal beams. installation, a 1 inch by I/S-inch strap will suffice. All Strap hangers may be hung directly on purlins or straps must be connected to the ductwork with beams when the duct is running transverse] y or across sheet-metal screws. On all government work, it is the purlins or beams, as shown in figure 2-101. required that the screws be placed 1 1/4 inches from However, the strap hangers must be twisted to turn 90 Figure 2-101.—Strap hangers from purlins. 2-35