Although the fittings consist of four components: Nut, back ferrule, front ferrule and the body, it becomes a four piece connection when affixed to tubing. The two ferrule design and sequential action of the fittings overcome in-variation of tube wall thickness and hardness to assure safe, reliable, leak-free connections PMT tube fittings are easily installed without any special tools. The front ferrule swages onto the tube as it moves down the cone of the body creating a pressure/vacuum tight seal on both tube and body by interface pressure and surface finish of matching components. The back ferrule, deforms into the tube creating a strong mechanical and anti-vibration hold on the tube. The internal diameter of body and nut are closely controlled which constrain the tube within a close tolerance of its axis ensuring accurate alignment within the assembled fitting. In case of S.S. tube fittings high hardness of ferrules of ferrules is assured / maintained (more than Rd 90 ) For reliable joints the positive tolerances on inside diameter of ferrules and body is kept to minimum. The nut threads are silver coated to ensure no galling |