A notch keeps the plunger in the retracted position.
.5-C-NI Indexing Plunger Type G and GK with threaded stem are for applications where a special knob or attachment is required, or for such cases where the spindle is linked directly to an operating mechanism.GN 817 indexing plungers with lock-out (Type C / CK) are used for applications where the plunger pin needs to stay in its retracted position.