507 ETRO was in the Promotional , I didn't make it Up but just quoted what was written by the Promoter ..

349 and 305 are both 16. 451 & 406 are both 20" its all about smaller rim fatter tire Vs larger rim and skinnier tire combined

both , can have the nominally similar Outside diameter ..

Same sort of deal as French 700 A,B & C , 650 A,B & C, tires thinner rims bigger nominal diameter remains the same..


China doing the Argon rich Low oxygen tig welding is something they already do.
most builders charge the tubes then Flood the tig welder bead with inert gas
and continue blowing Argon or other inert gasses till your bead cools