Abstract: The simplex orifice fitting includes a housing having a longitudinal bore therethrough and a plate carrier slot intersecting with the longitudinal bore. A plate carrier, having a circular bore, is slidably received in the plate carrier slot. An orifice plate, having a bore therethrough for the passage of fluid, is carried by the plate carrier. A seal ring is positioned around the orifice plate and received within the circular bore of the carrier plate. Centering pins within the housing are connected to the housing and located transverse to the longitudinal bore of the housing. The plurality of centering pins have an end capable of contacting the plate carrier in an operative position. A sealing bar is connected to the plate carrier and springs are positioned between the sealing bar and the plate carrier to permit relative movement therebetween. The springs force the plate carrier into contact with the ends of the centering pins to properly position the plate carrier in the operative position.