Ril Inserts are made from high quality stainless steel wire, with a diamond shaped cross section wound to the shape of a spring thread. The insert, which is larger in diameter than the tapped hole, is compressed during installation then allowed to spring back permanently anchoring the insert in the tapped hole. Because of its larger diameter the ril insert has a greater contact area and is normally stronger than the original thread. Recoil Inserts Free Run Metric