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.

Metric Bite Type Thread Specifications Size Tube OD (mm) Thread Size 4LL 4 M8x1 6LL 6 M10x1 8LL 8 M12x1 10LL 10 M14x1 12LL 12 M16x1 6L 6 M12x1.5 8L 8 M14x1.5 10L 10 M16x1.5 12L 12 M18x1.5 15L 15 M22x1.5 18L 18 M26x1.5 22L 22 M30x2 28L 28 M36x2 35L 35 M45x2 42L 42 M52x2 6S 6 M14x1.5 8S 8 M16x1.5 10S 10 M18x1.5 12S 12 M20x1.5 14S 14 M22x1.5 16S 16 M24x1.5 20S 20 M30x2 25S 25 M36x2 30S 30 M42x2 38S 38 M52x2 Thread Size = Male Thread OD (mm) x Thread Pitch (mm)

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 alone 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.

The stop edge causes a sharp increase in tightening forces which is clearly perceptible. After assembly, a visible collar of cut tube material must completely fill the space in front of the first cutting edge. With stainless steel tube and hose connections made from free cutting steel, the collar is less due to the harder material.

During assembly, it is necessary that the tube is held firmly against the stop in the inner cone of the fitting; if not, the cutting process will not take place satisfactorily. Reassembly can be performed an unlimited number of times.

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.