In response to serious technical errors in the 18th edition, the committee voted in January 2003 to withdraw the 18th edition, and reissue the 17th edition. The issue was safety, and API had no choice but to take this action. The next edition of 6A will be called the 19th edition. Contains errata and supplementary material.This specification was formulated to provide for the availability of safe, dimensionally and functionally interchangeable wellhead and Christmas tree equipment. The technical content provides requirements for performance, design, materials, testing, inspection, welding, marking, handling, storing and shipping by the manufacturer. This specification does not apply to field use or field testing of wellhead and Christmas tree equipment. Critical components are those parts having requirements specified in this document.