Snap Fastener Button

Snap button (also called,snap  fastener press stud, popper,  or  snap) is a pair of interlocking discs, made out of a metal or plastic, commonly used in place of buttons to fasten clothing and for similar purposes. 

Snap button is a kind of spring buckle, which is called S-type spring buckle (combined by the spring). is divided into four parts from top to bottom. The AB side is generally called female buckle. It seems that there are two parallel springs (actually the same one) on the side of a hole. The AB side is generally called the male buckle. It is clamped by the spring after being pressed into the hole of the female buckle to produce tension. The professional term is called opening and closing power.