No sag spring also named Zigzag spring,Sinuous springs,Upholstery springs,S shaped springs.Serpentine springs.A roll really resembles a continuous “s” curve which is somewhat heavy and difficult to unwind.
Springs are equally spaced and attached from the back to the front of the seat frame. A clip is attached to each end of a spring, then the clip is nailed, screwed or stapled into the seat frame.
After determining the length required and the number of pieces, the lengths of spring are cut from the roll with a wire cutter. There is a lot of pressure involved with this spring, whether in the original roll or in a cut length.
Sometimes this pressure can cause a frame to bend or warp. Because of this pressure, sometimes the frame has to be re-enforced to prevent the bending or warping.