I knew the brackets wouldn't work but had to be sure the outside diameter was correct since I have Square Tube frame the had an inside diameter of 1 5/8\" and the new guide tubes were 1.5\". Not a lot of leeway but teh discprotion was correct. Slid right in and if anything, a bit smaller than 1.5\" which was no issue. Actually, they look much better this way and almost like they are a part of the trailer. Just FYI if anyone has this issue of not being able to use the mounting brackets that probably work on the majority of trailers. The build looks strong and square tube is much better than the round tube ones that came with it when I bought. I did the same install with inner guides too.