This is the 1/4-20 Nylock nut that is used with the composite handle that comes standard on the Model D and E Indoor Rowers. The corresponding U-bolt is part number 244. Order two per handle. Also used in various places on the Model C and Dynamic Indoor Rower and all SkiErgs. See more info.
For use with Model D, E and Dynamic Indoor Rowers with manufacture dates from March 13, 2015–August 27, 2015. If the foot belly screws on your machine are loosening with use, this reinforcement kit will remedy the problem. Kit contains two triangular braces that reduce flexing of the foot belly, and 14 new style screws that are less prone to loosening.