ISO 10423:2003 specifies requirements and gives recommendations for the performance, dimensional and functional interchangeability, design, materials, testing, inspection, welding, marking, handling, storing, shipment, purchasing, repair and remanufacture of wellhead and christmas tree equipment for use in the petroleum and natural gas industries.

ISO 10423:2003 does not apply to field use, field testing or field repair of wellhead and christmas tree equipment.

ISO 10423:2003 is applicable to wellhead equipment (casing head housings, casing head spools, tubing head spools, cross-over spools, multi-stage head housings and spools), connectors and fittings (cross-over connectors, tubing head adapters, top connectors, tees and crosses, fluid-sampling devices, adapter and spacer spools), casing and tubing hangers (mandrel hangers, slip hangers), valves and chokes (single valves, multiple valves, actuated valves, valves prepared for actuators, check valves, chokes, surface and underwater safety valves and actuators, back-pressure valves), loose connectors [flanged, threaded, other end connectors (oec), and welded] (weld neck connectors, blind connectors, threaded connectors, adapter and spacer connectors, bullplugs, valve-removal plugs), other equipment (actuators, hubs, pressure boundary penetrations, ring gaskets, running and testing tools, wear bushings).

ISO 10423:2003 defines service conditions, in terms of pressure, temperature and material class for the well-bore constituents, and operating conditions.

ISO 10423:2003 establishes requirements for five product specification levels (PSL). These five PSL designations define different levels of technical quality requirements. It also provides guidelines (not requirements) for selecting an acceptable PSL.