These caps were printed using SainSmart TPU and will only work properly if printed using a flexible filament. The parameters at the top of the OpenSCAD file can be adjusted for different-sized bearing housings. For the prints in the picture, I had measured them, printed at that size, and then had to increase the size to 102%. I've adjusted the OpenSCAD file for that in the off chance you might have the exact same size of bearing housings as what was on this trailer, but in general, you will likely have to adjust the bearing OD a bit to get the print to fit snugly-but-removably over the end of your bearings.