UF Instructions

To make sure the flange fits

To control the inner duct-Ø please refer to the MRF measuring band instructions. In case of deviations beyond the tolerances, read the values on the scale and send us that information when placing your order.

Please advise upon ordering if the flanges are intended for fittings, as they are made smaller (diameter about 3 mm smaller / circumference about 9 mm shorter). The SR joining clip bridges 
these small diameter differences.


Before inserting the flange into the duct apply an adequate sealant into the groove of the flange along its entire circumference.

Another possibility: After the installation of the flange apply mastic inside the duct between the flange and the duct wall (not always possible with smaller ducts). The different sealing solutions can often be combined for more security.

Installed properly the air-tightness classes C and even D according to DIN EN 12237 can be reached.

Fitting the Flange

Place the flange in front of the duct end ( grip-pliers might be helpful) and drive the flange evenly home using a rubber hammer.

If the seam is too high (A) preventing the flange from being inserted all the way in, grind it down (B).

Fixation Possibilities

Alternative fastening methods: blind rivets or self-tapping screws.
Distance between the fixing points: between 50 and 100 mm.

Spot welding is not suitable.

When fixing start eitherat one end of the flange and work your way around . . .

or at the opposite point and work both on the left and right sides till you reach the flange ends.

CAUTION: If you start by fixing both flange-ends first, the duct may become wavy!

For further instructions please refer to the SR Joining Clips section.

Check the inner duct diameter

Fastening the UF flange on the round duct with blind rivets.


Screws are less recommended, as they protrude inside the duct, hindering the air-flow and the cleaning operations, and could be the cause of leakages.