We recommend keeping an extra knobs or wing nuts handy in case one gets lost.
The knob style has recently changed to the pictured knobs. (The old style larger, rounder knobs are no longer available.)
NEW TIP to keep your knobs on! Add some teflon plumbers tape to the threaded post, as shown in last photo. You can get this at any hardware store. It increases the friction and helps keep the knobs tight. Just add a little of the tape to the screw part and then put the knob on the harness. Works like magic to keep it from loosening.