These are printable wheels custom made to go with the V-slot aluminum rails from Open Builds. For use with a 3d printer or CNC Router. I have been using them on a CNC router and they have held up so far. You can see a picture of the total CNC build in the picture section. These are designed to be used with 5x16x5 bearing, I will provide a direct link to amazon where you can find the particular bearings that will fit.
5x16x5 Rubber Sealed Bearings: https://amzn.to/2OIcR8c
5x16x5 Double Sealed High Speed Bearings: https://amzn.to/2xq0aIA