DIN 3949:1998-02

DIN 3949 Flare Fittings & Dimensions Chart

Our comprehensive DIN 3949 Flare Fittings & Dimensions Chart provides the exact technical specifications required to convert a standard 24° metric cone fitting body into a highly reliable 37° flared tube connection [INDEX]. Governed by the historical DIN 3949:1998 standard, this specialized 3-piece assembly—comprising a metric union nut, pressure sleeve, and dual O-ring spacer ring—bridges the gap between traditional metric cutting-ring ports and high-vibration flare plumbing systems. Whether you are engineering severe fluid power systems or sourcing replacement parts for the Light (L) or Heavy (S) series, this sizing matrix delivers the precise metric threads, hex values, and component lengths needed to ensure a zero-leak, soft-sealed mechanical joint.

Why Engineers Rely on DIN 3949 Dimensions

Unlike standard metal-to-metal bite type fittings, the DIN 3949 design requires a seamless cold-drawn metric tube to be mechanically expanded to a 37° profile. This geometry distributes clamping loads evenly, providing superior fatigue life against intense system pulsations, high-pressure spikes, and physical machine vibration.

Use our master dimensions index below to match your exact tube outside diameter (OD) to its corresponding metric parallel thread interface and component sizing limits.

1 Scope

This standard applies to flared connection components and the corresponding bore form of the cutting ring connection according to DIN EN ISO 8434-1, as well as to tubes to DIN 2391, grade C, delivery condition NBK, which are used in conjunction with threaded stud connectors to DIN 2353 "Non-soldered tube fittings with cutting ring" and DIN EN ISO 8434-1.

2 Normative references

This standard contains provisions from other publications by means of dated or undated references. These normative references are cited at the respective places in the text, and the publications are listed below. For dated references, subsequent amendments or revisions of these publications apply to this standard only if they have been incorporated by amendment or revision. For undated references, the latest edition of the referenced publication applies.

DIN 2353 Non-soldered tube fittings with cutting ring – Complete fittings and overview

DIN 2391-1 Seamless precision steel tubes with special dimensional accuracy – Part 1: Dimensions

DIN 3859-1 Tube fittings – Part 1: Technical delivery conditions

DIN 3865 Tube fittings – 24° sealing cone with O-ring, for bore form W according to DIN 3861

DIN 53519-2 Testing of elastomers – Determination of the ball indentation hardness of soft rubber, International Rubber Hardness Degree (IRHD) – Hardness test on specimens of small dimensions, microhardness test

DIN EN ISO 8434-1 Metallic tube fittings for fluid power and general use – Part 1: 24° cutting ring fittings (ISO 8434-1:1994)

DIN ISO 4042 Threaded components – Electroplated coatings; identical with ISO 4042:1989

3 Dimensions, designation

Dimensions in millimetres

The design of the flared connection components need not correspond to the graphical representation (see Figure 1 to Figure 6); only the specified dimensions shall be complied with (see Table 1 and Table 2).

3.1 Flared fitting – Assembly

a) Connection with bore form of the cutting ring connection according to DIN EN ISO 8434-1.

Figure 1: Fitting with two O-rings; tube connection side of a flared fitting

3.2 Flared fitting – Individual parts

Surface of the O-ring grooves according to DIN 3865.

Figure 2: Flare adapter

Figure 3: Flare sleeve

Figure 4: Flare pressure ring

a) Geometry at manufacturer’s discretion

Figure 5: Union nut

a) Thread corresponds to thread of the union nut according to DIN EN ISO 8434-1. b) For cold forged union nuts, an overflow of max. 1 mm is permitted.

3.3 Designation

Designation of a flare adapter with fitted O-rings 1 and 2 of series (L) for tube outside diameter 15 mm made of steel (St):

Flare adapter DIN 3949 – L 15 – St

Upon special request, flare adapters may also be ordered and supplied without O-rings but with O-ring grooves. It is then the sole responsibility of the user to use a suitable O-ring. The designation of a flare adapter without O-rings 1 and 2 of series (L) for tube outside diameter 15 mm made of steel (St) is then:

Flare adapter DIN 3949 – L 15 – St – O

Designation of a flare pressure ring of series S (S) for tube outside diameter 20 mm made of steel (St):

Flare pressure ring DIN 3949 – S 20 – St

Designation of a union nut of series S (S) for tube outside diameter 38 mm made of steel (St):

Union nut DIN 3949 – S 38 – St

Table 1

Dimensions in millimetres

¹) Applies only for steel material, see Technical Delivery Conditions DIN 3859-1. ²) For the original equipment of flare adapters with O-rings, O-rings with deviating dimensions may also be used. The function of the flare adapter must still be ensured with these O-rings. For spare part supply, O-rings with the dimensions specified here shall be supplied.

Table 2

Dimensions in millimetres

表格

¹) See Table 1

4 Installation note

Tube length determination: The tube shall be shorter by dimension Y at each connection than the tube for a cutting ring connection. Dimension Y, see manufacturer’s specifications.

Figure 6: Tube length determination

5 Material

Flared connection components: Standard material steel according to DIN 3859-1. Other materials may be agreed upon with specification of the material short symbol and appended to the standard designation in place of "St".

O-rings: Standard material Acrylonitrile-butadiene rubber (NBR). Other materials may be agreed upon with specification of the material short symbol and appended to the standard designation. O-ring 1: Hardness (85±5) IRHD, O-ring 2: Hardness (70±5) IRHD, IRHD hardness according to DIN 53519-2.

6 Finish

Standard surface protection finish: A3C according to DIN ISO 4042.

7 Technical delivery conditions

In accordance with DIN 3859-1.