I used 1” conduit to build. The 3/8” pipe inserts made it possible to use all thread on the ends of the uprights so I could use some knobs to hold the sled to the frame and so I could break it down to transport if I want to. Pipe inserts on the bottom flanges and a 3/8” bolt keeps the frame tight to the ski’s. Pulls great behind the snowmachine and even better by hand.