One of the sewing methods, also known as "reverse sewing". That is, the common single-sided interlocking pins are buckled again relatively staggered. The first buckle is a stitch between stitches, and the second buckle is just inserted inside. The buckle edge is wider than the ordinary buckle needle and shaped like a braid. This method is often used to deal with buttons carved on both sides. Strong fastness, but more labor-consuming. Plastic mold thimble can also be used in the mold, which can play a stable role, also called insert needle. Inserting pins are inserted into the mold core to exhaust air or make the mold core better processed. According to different shapes, inserts can be divided into flat inserts, straight inserts and stepped inserts. In general, the insert is made of die steel such as SKD6 1 or SKH5 1.