Well, it is 3 inch diameter but I had good luck with RV sewer-drain hose. It is cheap and light, and has a good self-returning action- It will stretch as the wheels are turned and then take up the slack so it doesn't drag on the track. For end fittings I used some aluminum downspout adapters (where a downspout attaches to a house rain gutter.) Very cheap and light, too. It is NOT heat-resistant but is only carrying ambient-temp air to the brakes and did not touch any hot parts- I never had it melt. Joel