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Often referred to as metric fittings these fittings seal using the angled sealing surfaces (metal to metal) or the combination of metal to metal with O-rings. They are available in very light (LL), light series (L) or heavy series (S) The sealing face angles are either 24° with or without O-rings, or 24°/60° universal cones. Identification is made by measuring the thread size and also the tube outside diameter.
MALE: The measurements for the male are taken from the outside of the threads.
FEMALE: For the Female, the measurement is taken from the inside of the threads.
The below diagram shows both where to take measurements from and the size dimensions.