In a pre-engineered metal building system, steel columns, rafters and other metal building parts bolt together in frames to make the primary framing system.
Girts attach from column to column across the length of the frames. Purlins attach from rafter to rafter across the roof of the frames. This makes up the secondary framing system.
ECO steel buildings have ¼-inch thick steel "clips" welded strategically on the columns and rafters. These clips are used to fasten the girts and purlins to the primary framing.