Heavy duty, low profile machine movers, dollies, moving skates, with solid rollers. These will move your Bridgeport, lathe, or mill with ease. All steel is American made and locally sourced, and the skates feature all Grade 8 hardware for maximum strength. Each roller is made from solid chrome-moly tool steel, which is lathe turned for concentricity, drilled and bored, and then finish reamed for a close tolerance fit onto ½ inch diameter grade 8 shoulder bolts. A light coating of grease is all that is needed for smooth operation. This creates a much stronger and more reliable design than ball bearings. High load applications should use bushings, not bearings that can fail due to point loading. Bushings can handle much more weight than bearings, because the load is spread evenly over the entire surface area of the bushing. The 2” inch wide solid steel rollers are fully contained within the undercarriage of the skate. This not only makes them compact for storage, but it puts all of the weight straight down preventing any flexing of the frame or axles. The skates stand 1.75” high, which make them easy to get underneath any machine, and come threaded on the top for a 3/8-16 bolt to secure them to the bottom of a machine and keep them from slipping out. I tapped the hole on the small side, as to fit many different machines, but leaving the option open if you want to drill it out to tap it for a larger size bolt. If you want it tapped a different size, let me know and I can probably accommodate you. I machine each and every one of these skates myself, in my small machine shop in Ohio. This listing is for a set of 2. Thanks for looking!