An extension added to a short face-to-face valve to conform to standard API 6D (or ISO 14313: 1999) face-to-face dimensions. API 6D specifies requirements and gives recommendations for the design, manufacturing, testing and documentation of ball, check, gate and plug valves for application in pipeline systems.

A unit of pressure control equipment with a body and two different end connections used to connect together other pieces of equipment that could otherwise not connect. Sometimes used instead of a Double Studded Adapter because at least one of the units to which it connects has a studded flange connection.