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, a larger angle may be required.

The straps that are used as hangers may be fabricated from 1/8-inch plate. In a normal installation, a 1 inch by I/S-inch strap will suffice. All straps must be connected to the ductwork with sheet-metal screws. On all government work, it is the required that the screws be placed 1 1/4 inches from all edges, as illustrated in the figure which shows that the duct system hanging from angle rails and that allangles be either bolted or tack-welded to purlins or beams.

Strap hangers may be hung directly on purlins or beams when the duct is running transverse] y or across purlins or beams, as shown in figure 2-101. However, the strap hangers must be twisted to turn 90

Figure 2-101. - Strap hangers from purlins.