This international Standard gives tables of dimensions, in millimetres, and masses per unit length, in kilograms per metre, of plain end steel tubes. It covers two groups of tubes : - Group 1: tubes for general purpose use (see table 2); - Group 2: precision tubes (sec table 3). The outside diameters are classified into three series for group 1 and into two series for group 2. The classification of outside diameters and the selection of preferred thicknesses offers information on which tube dimensions should be selected for national and international standards for either general purposes or particular use and application. The use of this information Will ensure the selection of the most favourable dimensions for particular purposes. It should be noted that the inclusion in tables 2 and 3 of a mass for a given size of tube, which does not have a series 1 outside diameter and preferred thickness, does not necessarily mean that it is available. Should the mass of a tube of dimensions other than those given in tables 2 and 3 be required, it has to be calculated using the formula given in clause 4. This International Standard is not applicable to tubes primarily intended to be screwed in accordance with ISO 7-l! The masses of such tubes, both screwed and plain end, are given in ISO 65r21.