The J.W.Winco series GN817.3 have been developed to enable precise locating when guide bushings are used. A plain guide bushing is used whereby the dimension of the plunger determines the length of the bushing. Both components are hardened and ground. The bushing length influences the accuracy of the positioning. The version with rest position is used in such applications where the plunger must not protrude continually. In that case, the knob is retracted and then turned by 90°. A notch prevents the plunger from turning by error or vibration.