The mold consists of three basic parts, namely, the floating cavity plate and the fixed template in the dynamic simulation part. The aperture of the push plate should be slightly larger than the diameter of the core wire to prevent the thread from being scratched. The assembly mechanism is an injection molding machine consisting of a push plate, a push semi-fixed plate and an ejector rod. The distance from the floating cavity plate controls the maximum movement limit of nails or similar devices. The principles of injection molding and casting are very similar. When the resin material enters the rotating screw, it should enter three separation zones: feeding zone, compaction zone and plasticizing zone. The gate is the entrance of molten plastic into the cavity, and the shunt wall must be smooth to prevent the shape resistance of parting surface when the melt flows, which depends entirely on the shape contraction of plastic, making it difficult to eject plastic parts. During injection cooling, shrinkage depends on the melting process of plastic parts.