Metric Bite Type Thread (MBT)

The flareless bit type fittings was pioneered in Germany in the early 1930's. Today MBT fittings are the most widely used bite type fittings in the world.

The MBT progressive ring fitting is a flareless metric fitting (for metric tube) that consists of a body, a progressive ring (ferrule), and a nut. On assembly, 2 cutting edges of the progressive ring "bite" into the outer surface of the tube ensuring the necessary holding power and seal for high operating pressures. 

Figure 1 - MBT fitting components: Body, ferrule, and nut 

Three series of MBT tube fittings (LL, L, and S) and accessories are manufactured in accordance with DIN 2353 on the basis of decades of experience.

How MBT Fittings Work: Function of Progressive Ring Fittings

The MBT progressive ring fitting produces a low to high pressure leak free connection of tubes and components in fluid systems. The basic function of the MBT progressive ring is the controlled progressive bite of the ring into the tube due to a unique internal geometry.

The front cutting edge has already started cutting into the tube before the second cutting edge starts. As soon as both cutting edges have cut the tube to the designed depth, further advance is limited by the stop edge.

Owing to the design of both cutting edges and stop edge all forces arising are equally distributed. This distribution along with the specially designed interior collar of the ring guarantees increased safety, particularly with regard to vibration and flexure stresses. The design and function of the progressive cutting ring ensure that service vibration loading is not present in the areas of the tubing where the bite is made. 

Preset of Progressive Ring 

The MBT fitting requires a preset operation that creates a bite by the progressive ring into the outer surface of the tube. You can do this manually with the fitting body.
Presetting with the fitting body is only recommended for steel and copper tubes.

Steps for Presetting Using the Fitting Body 

1. Lubricate thread and cone of fitting body as well as the progressive ring and nut threads.
   
2. Slip nut and progressive ring over tube, assuring that they are in the proper orientation.
   
3. Screw nut onto fitting body until finger-tight or light wrench resistance. Hold tube against the shoulder in the cone of the fitting body.
   
4. Mark nut and tube in the finger-tight or light wrench resistant position.
   
5. Tighten nut 1½ turns. The tube must not turn with the nut. The stop edge in the progressive ring limits over tightening by sharply increasing the tightening torque.
   

Preset Inspection

To inspect the preset, remove the nut and tube from the fitting and check if a visible collar fills the space completely in front of first cutting edge. If not, tighten slightly more. It does not matter if ring can be rotated on tube end.

Installation

To install the preset tube assembly to the fitting body, wrench-tighten nut to wrench resistance (light wrenching). From this position, tighten nut another ¼ turn or 1½ flats of the nut. Another wrench must be used to prevent movement of the fitting body.