This document 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 tree equipment for use in the petroleum and natural gas industries. This document does not apply to field use or field testing. This document does not apply to repair of wellhead and tree equipment except for weld repair in conjunction with manufacturing. This document does not apply to tools used for installation and service (e.g. running tools, test tools, wash tools, wear bushings, and lubricators). This document supplements API Spec 6A, 21st edition (2018), the requirements of which are applicable with the exceptions specified in this document.