Round Flanges LF

LF Circular Flanges

Flange connection for ducts and fittings with turned out edges (Van Stone).
For duct-Ø 200 up to 3000 mm.
In galvanized and stainless steel
Rapid installation, as the flange is simply snapped on the turned-out edge.
Smooth inner surfaces; no projections inside the duct.
Especially suitable for fittings.
Assembly through SR Joining Clips.

  1. Duct wall
  2. Turned out edge (Van Stone).
  3. LF circular flange
  4. Tapered opening with injected sealant HD (no sealant with the LF in V2A)
  5. SR joining clip

Suitable Ducts

For inner-duct diameters from 200 up to 3000mm. In-between diameters are also available. IMPORTANT: Please indicate if flanges are intended for fittings, in which case their Ø is made 3 mm smaller.

Suitable for ducts and fittings with a turned-out edge (Van Stone).

Not suitable for: spirally wound ducts, longitudinal seam ducts and ducts with stiffening ribs.

Fixation Methods

Rapid and easy flange installation, as the flanges are simply snapped on the turned-out edge of the duct.

No fixation methods are necessary.


When correctly installed the air-tightness class C (DIN EN 12237) or ATC 3 (DIN EN 16798-3) are reached. See also ZI-702.

No projections inside the duct (ideal for the extraction of chips, fibers, etc.).   

To reach the air-tightness class C no additional measures, such as the use of adhesive tapes, sealants or mastic, are necessary. The necessary SR Joining Clips must be ordered with gasket.

Available in galvanized steel. Stainless steel V2A (1.4301 ASTM 304) and V4A (1.4404 ASTM 316) upon request. There are a few technical differences between the flanges in galvanized steel and the ones in stainless steel. Please refer to information on metals (ZI-101) and the page about the LF flange dimensions.



Does not provide any additional stability or stiffness to the duct, especially under negative pressures.

Stainless steel versions must be sealed as these are delivered without sealing compound in the tapered slot.


Installation Instructions

LF Installation Video

Screws or Rivets?



STP Documents


Equipotential Bonding