This product is paramedic, so you can change it to fit with whatever wheel size you have. The material costs less around $1 for my wheel size, and will vary slightly with how big of a wheel you print it for.
Both pieces are press fit into inner cylindrical surfaces of the wheel rubber. The hole in the back rim it about 1/16 inch bigger radius than the radius of the cylindrical piece of the cast aluminum tuck. This blocks almost all water and debris from entering the back side of the wheel. The front side is an even better seal, as there is a solid surface blocking any water or debris from entering.