US Patent 7538568 Spring loaded probe pin

A conductive plunger 3 is received inside a cylindrical conductive barrel 2 so as to be capable of moving backward and forward, an urging coil spring 4 for pushing a rear end 3b of the plunger 3 is received inside the barrel 2, and a front end 3a of the plunger 3 is protruded from an opening at one end 2a of the barrel 2. In this probe 1, stable electrical contact is achieved by inserting a conductive coil spring 5 that does not urge the plunger 3 between the inner circumference of the barrel 2 and the outer circumference of the plunger 3 to realize electrical contact between the inner circumference of the barrel 2 and the outer circumference of the plunger 3 via this coil spring 5.