The tubes will be designated by the following symbols: a) the letter T; 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, indicative of its galvanized condition; d) a letter indicative of the condition of the ends, according to the following code: R = Threaded L = Smooth e) the designation of this standard.