These are the little plastic retainer washers that help to hold the camera mounting knob (CMK) and vertical rail mounting knob (VRMK) in place for NN3/NN4/NN5 series pano heads. And we'll also incude a few extra rubber O rings as well which help prevent metal to metal wear.
Price includes little baggy of 10 ea. retaining washers.
Note: "unscrew" knob from retaining washers when removing knobs to maintain its effectiveness.