Some Features of the Metric Thread Bite Type Tube Fitting

The double ferrule fitting

The double ferrule fitting is one typical kind of metric thread bite type tube fittings. As the name refers, the double ferrule fitting has the ability to lock onto the tube with a 'double bite' feature, it is to securely join tubes together in a seal tight assembly. Each ring bites in to the tube giving two separate sealing areas. This style of fitting does so without transmitting torque or twisting the tube ensuring that the tube does not become 'stressed'. Therefore, the mechanical properties of the tube are maintained.

The wear problem of fittings

With the use of SAE stainless steel adapter, brass adapter or aluminum adapter, the wear problem is resolved by the use of silver plating. The internal parts of the nut are the only areas that are plated. Materials such as high Nickel alloys, high temperature alloys, duplex and super-duplex's are coated with an anti-wear agent in the same way. For chemical stability issue, the ideal situation is that both tube and fittings are manufactured from the same material type.

The assembly instructions of fittings

There are strict assembly instructions to follow with metric thread bite type tube fitting. The rule states that for the majority of sizes 1-1/4 rotations of the nut, from the finger tight position, will give the correct seal tight assembly. It is permissible to further 'snug' the fitting if a minor leak appears but this is normally unnecessary. When access to any system is required, these metric thread bite type tube fittings provide an excellent 'break-in' point. The joint can be made and re-made many times over without loss of sealing integrity.

About the wall thickness of the tube to be connected

The strength of the fitting is such that the tube contained will burst before the fitting shows any sign of a leak or movement. This is more or less affected by the wall thickness of the tube. If the wall is too heavy the rings will not bite as well, as when the tube wall is too thin, the tube will collapse rather than allow the rings to bite fully. Therefore, reference to the manufacturers' product information should be made in all instances.