I adapted this to be used on a 3 inch wide tube. Essentially I heated up the metal with some map gas, and then straightened out the little dog leg on each support some with a 3lb sledge hammer and anvil.  This allow me to use the existing four-inch keel roller. Took about 15 min. to modify, and then I painted the entire thing with black enamel to match my trailer. My only complaint is it only came with one axle or pal nut, and the 5/8 diameter ones are not easy to come by at the local hardware store. I ended up ordering a few off of eBay which cost me an extra five dollars with shipping. I guess I could have sent this back, but I just wanted to be done with it. The rubber is a little bit soft, but keel rollers are only about four or five dollars to replace, and they do tend to harden over time by themselves. If you put a lot of weight on this from the get-go you may end up with a flat spot, so be advised.