Quality OKE clip knot (no sag spring parts),zigzag spring,sinuous spring,coil ... spring,sofa spring,seat spring,no sag spring. OKE clip knot (no sag spring parts), zigzag spring,no sag spring,sinuous ... commonly used: (pitch:18,loop height:48)(2) OKE clip knot (used with no sag spring) 1).high-tech plastic material ... are made especially for loose cushion upholstery. OKE clip knot (no sag spring parts)