Because the lower crotch seam is a larger internal arc, only when it is opened here, the seam will change the line shape and form a curve similar to the human leg shape.

Besides, the length of the front and back crotch of trousers is different from that of trousers and fabrics.

For example, the front and lower crotch joints without elastic material and straight trousers should be longer than 0.7 to 1 cm in the lower crotch seam; the lower crotch joints with elastic material, bell bottoms and body tights should be longer than 1.5 to 2 centimeters in the lower crotch seam.

Therefore, when playing the board, we must pay attention to trousers and pants fabrics, to specific problems specific analysis, can not be generalized, otherwise the pants may not be the same.