In the process of doing some maintenance on a family member's trailer, the grease fittings on the axles were exposed to dust, dirt, and general road grime and had to be cleaned to be able to properly grease the bearings. The trailer had bearing protectors but every one of them was missing their protective cap. Now that the trailer has these covers on the bearings, that problem is unlikely to recur. This model is designed to be printed using a flexible filament so as to stretch over the outside of the bearing. It's designed with a small relief near where the end of the bearing housing sits so the cover can be pushed all the way on and not be constrained by the flat end.