close, micrometer puts it at .4382, so just about 7/16ths. Guy at the shop that I had it cut down at said he ran some stamping number he found in the tube, it was a heavy duty version out of a 79 W350 dually. Said something about double ribbing but I'm not sure what he meant. having trouble getting good weld penetration with my Mig, gonna grind off my tack welds and switch to my stick welder, I've welded up to 3/4 with it before so it should do the job.