The Tension Adjustment knob screws down on top of the large bolt/spindle which comes through the center of the arm cord DRUM. Below this knob is a SPRING and WASHER - BEARING - WASHER which sits on top of the arm exerciser cord drum.
ALL of our original OEM knobs come triple reinforced which we do here. Plastic around the threaded insert has been heat sealed with 3 layers of rubber tubing which we apply by hand one layer at a time.
We also have LEGACY Tension adjustment knobs which are not as prone to breakage or cracking. We offer a LIFETIME warranty on those.