[sanddrag]

Our frame for the past three years has been 6063 box tubing because that's all the local supplier stocks. Works just fine, never had a problem, and polishes pretty nicely. On occassion, we'll get metal from McMaster or other online source if it is something we need that the local place doesn't stock. We used 6061 axles this past year. they were cantilevered out a fair distance. Bearings were <1" apart. Axle was 5/8" dia between the bearings and 1/2" for the rest. The only problem we've evperienced with 6061 axles is the keyway getting some backlash after a while.