This European Standard specifies basic connection dimensions of LPG cylinder valves (manufactured in accordance with EN ISO 14245 and EN ISO 15995) and connectors (including pressure regulators) to enable them to be safely connected together. This European Standard lists potentially unsafe connections where it may be possible to connect together, but which when connected may not be sound or secure in some operating conditions or orientations. This European Standard identifies a marking system that is intended to ensure that only valves and connecters that are marked with the same connector type number are used in combination. This European Standard also recommends tightening torques for the attachment of screwed metal-to-metal connections. Quality assurance systems, production testing and particularly certificates of conformity are not covered in this standard. This European Standard excludes connections for automotive vehicles covered by UN/ECE Regulation No. 67 Part 1 and EN 13760. This European Standard excludes connections for gas cartridges covered by EN 417.