As a basic standard for dimensional standards for weld-on valves, this standard applies to end-to-end and centre-to-end dimensions and their permissible deviations. The standard defines the end-to-end and centre-to-end dimension and sets out series from which the end-to-end or the centre-to-end dimensions required in the individual dimensional standards must be selected. When standardizing the individual valve design types, end-to-end or centre-to-end dimensions shall only be taken from one series.