Heavy duty, low profile machine movers, moving skates/dollies, with a solid roller “bushing” type design, (no ball bearings to fail). I hand make all of these skates using all American made steel that is locally sourced, and the skates feature all Grade 8 hardware for maximum strength. Each roller is made from solid chrome-moly tool steel, which I lathe turn for concentricity, drill and bore, and then finish ream for a close tolerance fit onto 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 cheaper units that use ball bearings. High load applications should always use bushings, not ball bearings that can fail under load 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, vs the point loading of ball bearings. The 2.25” inch wide solid steel rollers are fully contained within the undercarriage of the skates, putting all of the weight straight down, preventing any flex in the axles. The skates only stand 1.75” high, which make them very easy to get under any machine, and the top is threaded in the center for a mounting bolt to secure them to the bottom of a machine, to keep them from kicking out. I personally make each and every one of these skates by hand, using all manual lathes and mills in my small home shop in Ohio. This listing is for a set of four (4) skates. Thanks for looking!