These bolt on wheels were just what I needed for my back problem. My little Craftsman air compressor was heavy enough to knock me over every time I had to lug it around pumping up car tires in my driveway. I filled all the tires, lugged that heavy compressor to each wheel, and then my back hurt for several days. After inspecting the 3 metal legs on the compressor, I noticed holes already drilled into their base. The threaded shaft on these wheels fits perfectly through the holes. Lock washers and screws are all you need for an air compressor. These large-diameter wheels with soft-cushioning treads roll effortlessly through every crack and crevice in garages and driveways. Me and my back highly recommend this product.