Principles of design, materials of components, dimensions and construction, marking, testing and reports to be supplied to the purchaser. Appendices on safe-guarding, periodic re-checking, overhaul and re-test, on measurement of slackness of fit of closure ring and body threads, and on safe use.Cross References:BS 18:Part 1BS 131:Part 1BS 817BS 1503BS 1580:Parts 1 & 2BS 1780BS 3643:Part 1BS 3643:Part 2