API Specification 6A specifies requirements and gives recommendations for the performance, dimensional and functional interchangeability, design, materials, testing, inspection, welding, marking, handling, storing, shipment and purchasing, of wellhead and christmas tree equipment for use in the petroleum and natural gas industries.

This edition of API Spec 6A is the modified national adoption of ISO 10423:2003, Petroleum and natural gas industries-Drilling and production equipment-Wellhead and christmas tree equipment. An informative annex is included covering the requirements of the API Monogram Program for equipment covered in the specification.