Flange facings: RF, FF and RTJ

Raised Face (RF) is the most common. The raised face is 1.6 mm for Class 150 and 300 and 6.4 mm for Class 400 and above.

Flat Face (FF) is used against cast-iron equipment and with full-face gaskets, so bolting does not crack the mating flange.

Ring Type Joint (RTJ) uses a machined groove and a metal ring gasket (R, RX or BX) for high pressure and temperature.

Surface finish for spiral-wound gaskets is normally 3.2–6.3 µm Ra (125–250 µin AARH) with a concentric or spiral serration.