Knowledge · Connection Technology
Flare or Cutting Ring: Choosing the Right Tube Fitting
Flare or cutting ring is the fundamental decision as soon as a tube has to connect leak-tight to a hydraulic line. Both are reusable, metal-sealing tube fittings, but they get there by different routes: the cutting ring per DIN 2353 bites into the unformed tube, while the 37° flare forms the tube end itself into a sealing cone. The choice is not decided by the price of a single fitting, but by two questions: is flaring equipment in-house, and how high are pressure and vibration in the line.
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How each one seals
The cutting ring fitting seals on a 24° internal cone. As the union nut is tightened, the hard cutting edge of the ring is pushed over the cone and bites into the tube outside diameter. Ahead of the edge it raises a visible collar that holds the tube axially and, per Parker, creates a spring effect that absorbs pressure surges and bending cycles. The seal is metal-to-metal between ring, cone and tube, with no tube forming at all: the tube is only cut to length and deburred. The series of this design are explained in the article on the DIN 2353 series.
The flare fitting seals on a cone that you form on the tube end beforehand. A flaring tool widens the tube end to 37°; this flare cone seats metallically against the 37° cone of the fitting when tightened, and the union nut only provides the clamping force. The 37° flare is standardized as a JIC fitting per SAE J514 and ISO 8434-2, and dominates in mobile hydraulics. The seal sits on the formed tube, not on a separate ring.
Both designs belong to the same standard family, DIN EN ISO 8434: the cutting ring to part 1, the 37° flare to part 2, the O-ring face seal ORFS to part 3 and the 60° cone connection to part 6. What matters is the practical consequence: the systems are not mixable. A 24° cutting ring body does not accept a 37° flared tube, and the union nuts differ. If you switch, you replace the whole connection, not just one part.
Decision criteria side by side
Both systems are mature and at home in the high-pressure range. The table below sets out the criteria that decide the choice in practice. Where the data supports firm figures, they are in the row; otherwise the comparison stays deliberately qualitative.
| Criterion | Cutting ring (24°, DIN 2353) | Flare (37°, JIC) |
|---|---|---|
| Vibration | spring effect of the cutting edge damps pressure surges and bending cycles | metal flare cone without spring effect; support strong vibration with tube clamps |
| Wall thickness | wide wall-thickness window per series; a minimum wall is needed so the cutting edge holds and does not crush the tube | tube end must be cold-flarable; very thin, very thick or hard tube limits flaring |
| Assembly effort | pre-assembly required, turn-controlled; no forming tool for small sizes | extra flaring step per tube end with a flaring tool, then just tighten the nut |
| Reusability | body reusable; the ring stays on the tube, repeat assembly possible | the formed tube end is retained and can be reconnected many times |
| System pressure | high: up to 500 bar (series L), up to 800 bar (series S) | medium to high pressure range, depending on size and standard |
| Prevalence | European standard of stationary industrial hydraulics | common in mobile hydraulics and internationally influenced plant |
In practice, two rows usually decide it. If no flaring tool is at hand or tube sizes change often, that argues for the cutting ring, because it needs no forming. If the plant is already built around JIC or the line vibrates strongly, that argues for the flare. The remaining criteria sit close together and rarely tip the decision on their own.
Typical applications
In most stationary industrial plant the cutting ring fitting leads; the flare fitting plays to its strength where flaring equipment is present and the line vibrates strongly. Map your plant to one of the two cases. If the application needs maximum fatigue strength without a metal sealing point, the ORFS fitting is worth a look as a third design in connection technology.
A cutting ring fitting per DIN 2353 fits when:
- stationary industrial hydraulics, machine building and plant engineering per DIN 2353 are called for.
- you assemble without flaring equipment: the tube is cut to length, deburred and pre-assembled on site.
- mixed tube sizes and repairs are due where no forming tool is at hand.
- high system pressures into the range of the heavy S series are required.
A flare fitting with a 37° flare fits when:
- the plant is already built around 37° flare or JIC.
- a flaring tool or flaring machine is available in-house.
- lines vibrate strongly and the formed tube end is preferred.
- existing JIC systems are replaced or extended without mixing standards.
Many plants run both systems side by side. In that case standardize per line or assembly, not per plant: keeping one line entirely on cutting ring or entirely on flare avoids adapters, mismatches and extra leak points. For stainless steel and aggressive media both designs are available; the material choice for body, ring and seal follows the medium and environment, not the sealing principle.
Tube fittings from stock
PTS carries cutting ring, flare and ORFS fittings as a catalog program, from stock and matched to tube outside diameter, series and port thread. For the pairing, PTS technical support helps: it sizes the right connection and supplies the fittings to go with it.
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