when a sprue allows the melt plastic material to flow into the cavity, that is called direct gate, in that case, the plastic part will be left with a trace by the sprue. To keep the sprue bush in place, while being under pressure, a step design is used to fix it on a locating ring. The hole inside the spure bush is usually conic in shape. The smaller end of the hole is a curve, the larger taper the hole has, the easier the spure to pop out. Spure bush and nozzle may come in contact on a planer surface, it facilitates a right location and tight fit.