This Recommendation: a) gives the characteristics of gas discharge tubes used in accordance with [b-ITU-T K.11] and [b-ITU-T K.46] for the protection of exchange and outdoor equipment@ subscriber or customer equipment and telecommunication lines against overvoltages; b) deals with gas discharge tubes having two or three electrodes; c) does not deal with mountings and their effect on tube characteristics (see [ITU-T K.65]); characteristics apply to gas discharge tubes as a component@ mounted only in the ways described for the tests; d) does not deal with mechanical dimensions; e) does not deal with quality assurance requirements; f) does not deal with gas discharge tubes which are connected to electrical power systems.