Do you mean the choke cable (knob)? If you have the stock cable with the "pull" knob mounted below and to the left of the speedo, then the small round shoulder, on top of the choke knob bracket, will turn clockwise to tighten up on the cable to help hold it's position. It's the small round shoulder piece on TOP of the bracket. The plastic nut below the bracket simply secures the cable to the bracket. The top shoulder is actually two seperate pieces, the inner piece works with the nut below to secure the cable to the bracket, while the outer piece on the upper side threads over the fixed shoulder and pinches down on the cable as it is tightened. The original would have had a rubber cap that fits snuggly over this knurled knob. No need to pull this rubber cap, just grasp it with your fingers and give it a turn (no tools, finger torque is plenty here, these parts are plastic). Often the rubber will disintegrate, leaving the knurled knob exposed (which will still work fine). If this top shoulder piece is showing threads, then the knurled, plastic pinch cap also rotted off and you would need a new cable.
