What is it? These are 1" thin height nylon threaded lock nuts that attach the rear wheels of the axle of a Mainstreet Pedicab.
Why do we love it? These are easy to adjust and tend to last a 2+ years.
Pro Tip! It is VERY important to maintain these. As soon as you notice this nut losing its nylon threading and its grip, replace it. Also, check the tightness of the wheel by pulling on the center of the rear hub. Once there is no space left, stop tightening. Over-tightening can shift the axle.
What are the options? These come in pairs.