The tubes will be designated by the following symbols: a) the letters TZ; b) the nominal diameter; Alternatively, the nominal diameter can be replaced by the average external diameter followed by the nominal wall thickness separated by a hyphen; c) the letter G indicating its galvanized condition; d) a letter indicative of the condition of the ends in accordance with the following code: R = Threaded L = Plain e) the designation of this standard Example: Seamless pipes of nominal diameter 1/2 with threaded ends