DIN 2353 Tube Size Chart – L, S & LL Series Dimensions

 

DIN 2353 is a widely used standard for metric tube fittings and tube connections, particularly in hydraulic, pneumatic, lubrication, and industrial fluid systems. The standard defines dimensional and functional requirements for compression-style fittings designed to connect metric tubes safely under pressure.

A typical DIN 2353 connection uses a 24° cone fitting design combined with a cutting ring or other sealing element. When the fitting is assembled, the ring grips the outside surface of the tube and creates a mechanically secure, pressure-resistant connection. This design allows tubing systems to be assembled without welding, making installation and maintenance relatively straightforward.

One of the most important considerations when working with DIN 2353 fittings is selecting the correct tube outside diameter (OD), wall thickness, and fitting series. DIN 2353 systems are generally classified into three series:

• LL – Extra Light Series
• L – Light Series
• S – Heavy Series

Each series is intended for different pressure ranges and applications. The L and S series are particularly common in industrial and mobile hydraulic systems.

A DIN 2353 tube size chart helps engineers and technicians identify compatible tube dimensions for these fittings. Typical metric tube outside diameters range from small instrumentation sizes such as 4 mm and 6 mm to larger hydraulic tubing sizes such as 38 mm and 42 mm, depending on the fitting series.

Understanding these dimensions is essential because DIN 2353 fittings are based primarily on the actual outside diameter of the metric tube, rather than a nominal pipe size.

This guide explains DIN 2353 tube sizes, fitting series, tube dimensions, wall thicknesses, and the key considerations for selecting tubing for hydraulic and industrial systems.

1. What Is the DIN 2353 Standard?

DIN 2353 is a German standard covering compression fittings with a 24° cone connection for use with metric tubes. The fitting system became widely adopted for hydraulic and industrial fluid applications because it provides strong mechanical tube retention while allowing connections to be assembled and disconnected without welding.

DIN 2353 fittings are commonly used in:

• Hydraulic power systems
• Mobile hydraulic equipment
• Machine tools and industrial machinery
• Lubrication systems
• Process equipment
• Agricultural and construction machinery
• Marine equipment
• Industrial fluid and gas systems

The fundamental feature of a DIN 2353 fitting is its 24° internal cone.

In a traditional cutting-ring connection, the fitting typically consists of a fitting body, cutting ring, and nut. During assembly, tightening the nut forces the cutting ring against the 24° cone of the fitting body. The cutting edges of the ring engage the tube surface, producing both mechanical retention and sealing.

This can be represented conceptually as:

Metric Tube → Nut → Cutting Ring → 24° Cone → Fitting Body

Correct tube dimensions are therefore critical. The fitting must match the actual tube outside diameter. For example, a fitting specified for a 12 mm tube is intended for tubing with a nominal outside diameter of 12 mm, not an approximately equivalent inch tube.

DIN 2353 Fitting Series

DIN 2353 fittings are traditionally divided into three main series:

Series	Description	Typical Application
LL	Extra Light	Low-pressure and lubrication systems
L	Light	General hydraulic and industrial systems
S	Heavy	High-pressure and severe-duty hydraulic systems

The L series provides a balance between fitting size, weight, and pressure capability and is therefore widely used in general hydraulic systems.

The S series uses a heavier fitting design and is intended for applications where higher pressure capability or greater mechanical strength is required.

The same tube OD may sometimes be available in more than one fitting series. For example, a particular metric tube diameter may have both an L-series and S-series fitting, but the fittings themselves are not necessarily interchangeable because their dimensions and pressure capabilities differ.

DIN 2353 and ISO 8434-1

DIN 2353 is closely associated with ISO 8434-1, which covers metallic tube connections using 24° cone connectors. Modern fittings are therefore often described by manufacturers as complying with DIN 2353 / ISO 8434-1.

For engineering and procurement purposes, the applicable edition of the standard and the manufacturer’s specifications should always be checked, particularly for:

• Tube OD
• Tube wall thickness
• Fitting series
• Material
• Working pressure
• Temperature
• Tube tolerances
• Assembly requirements

These parameters work together to determine whether a DIN 2353 tube connection is suitable for a particular hydraulic or industrial application.

2. DIN 2353 Tube Size Terminology

Understanding DIN 2353 tube sizes requires several basic dimensional terms. Unlike nominal pipe systems, DIN 2353 fittings are primarily identified according to the actual outside diameter of the metric tube.

For example, a DIN 2353 fitting designated for a 12 mm tube is designed to connect to tubing with an outside diameter of 12 mm.

Tube Outside Diameter (OD)

The outside diameter (OD) is the most important dimension when selecting a DIN 2353 fitting.

Metric tubing is normally specified in the following format:

Tube OD × Wall Thickness

For example:

12 × 1.5 mm

This means:

• Outside diameter = 12 mm
• Wall thickness = 1.5 mm

The fitting size is selected primarily according to the 12 mm tube OD.

Common metric tube outside diameters used with DIN 2353 fittings include:

4, 6, 8, 10, 12, 14, 15, 16, 18, 20, 22, 25, 28, 30, 35, 38 and 42 mm

However, not every diameter is available in every DIN 2353 fitting series.

Tube Wall Thickness

Wall thickness is the distance between the outside and inside surfaces of the tube.

Common hydraulic tube wall thicknesses include:

• 1.0 mm
• 1.5 mm
• 2.0 mm
• 2.5 mm
• 3.0 mm
• 4.0 mm

Wall thickness has a major influence on the tube’s pressure capability. For the same outside diameter, increasing the wall thickness generally increases the pressure capability while reducing the internal flow area.

For example:

Tube Size	OD	Wall Thickness
8 × 1	8 mm	1 mm
10 × 1.5	10 mm	1.5 mm
12 × 1.5	12 mm	1.5 mm
16 × 2	16 mm	2 mm
25 × 3	25 mm	3 mm

These dimensions describe the tubing itself and should not automatically be interpreted as the only wall thicknesses permitted for a particular fitting or pressure rating.

Tube Inside Diameter (ID)

The inside diameter (ID) determines the available flow area inside the tube.

It can be calculated from:

ID = OD − (2 × Wall Thickness)

For a 12 × 1.5 mm tube:

ID = 12 − (2 × 1.5)

ID = 9 mm

Therefore, the tube has:

• OD = 12 mm
• Wall thickness = 1.5 mm
• ID = 9 mm

The ID is particularly important when calculating flow velocity and pressure drop.

Metric Tube Size vs. Nominal Pipe Size

DIN 2353 tubing should not be confused with nominal pipe sizes such as NPS or DN.

A 12 mm DIN tube means the actual tube OD is approximately 12 mm. By comparison, DN pipe designations are nominal sizes and do not directly represent the actual outside diameter.

This distinction becomes especially important when selecting fittings, adapters, or transitioning between tubing and piping systems.

---

3. DIN 2353 Tube Series: LL, L, and S

DIN 2353 fittings have traditionally been divided into LL, L, and S series. The series classification helps distinguish fittings intended for different service conditions and pressure levels.

In general:

Series	Meaning	Typical Service
LL	Extra Light	Low-pressure applications
L	Light	General hydraulic service
S	Heavy	Higher-pressure hydraulic service

The fitting series affects more than pressure capability. It can also affect fitting dimensions, thread sizes, wall thickness requirements, and the overall robustness of the connection.

LL – Extra Light Series

The LL series is intended primarily for relatively low-pressure applications.

It may be found in systems such as:

• Lubrication lines
• Grease systems
• Low-pressure oil circuits
• Pneumatic systems
• Auxiliary fluid lines

Typical LL tube sizes are concentrated at the smaller end of the metric tube range.

Because modern hydraulic installations commonly require higher pressure capability, the LL series is less widely encountered than L and S in many hydraulic applications.

L – Light Series

The L series is one of the most commonly used DIN 2353 fitting series.

It provides a practical balance between:

• Pressure capability
• Fitting size
• Weight
• Installation space
• Cost

The L series is widely used in general industrial and mobile hydraulic systems.

Typical tube ODs associated with the L series include:

6, 8, 10, 12, 15, 18, 22, 28, 35 and 42 mm

These sizes form one of the most recognizable DIN metric hydraulic tubing sequences.

S – Heavy Series

The S series is designed for more demanding hydraulic service.

Compared with L-series fittings, S-series fittings generally have a more robust design suitable for higher pressure levels and severe operating conditions.

Typical applications include:

• High-pressure hydraulic power units
• Construction machinery
• Heavy industrial machinery
• Hydraulic presses
• Marine hydraulic equipment
• High-load mobile hydraulic circuits

Common S-series tube ODs include:

6, 8, 10, 12, 14, 16, 20, 25, 30 and 38 mm

L Series vs. S Series Tube Sizes

The dimensional sequences of the two series are different.

L Series	S Series
6 mm	6 mm
8 mm	8 mm
10 mm	10 mm
12 mm	12 mm
15 mm	14 mm
18 mm	16 mm
22 mm	20 mm
28 mm	25 mm
35 mm	30 mm
42 mm	38 mm

This distinction is useful when identifying an unknown DIN 2353 fitting.

For example, 15 mm and 18 mm are characteristic L-series tube sizes, while 14 mm and 16 mm are commonly associated with the S series.

However, the series should never be identified from tube OD alone. The fitting body, thread, pressure rating, material, and manufacturer’s dimensional information should also be checked.

---

4. Complete DIN 2353 Tube Size Chart

The following chart summarizes the commonly recognized metric tube outside diameters associated with the DIN 2353 LL, L, and S fitting series.

DIN 2353 Tube OD Chart

Tube OD (mm)	LL Series	L Series	S Series
4	✓	—	—
6	✓	✓	✓
8	✓	✓	✓
10	—	✓	✓
12	—	✓	✓
14	—	—	✓
15	—	✓	—
16	—	—	✓
18	—	✓	—
20	—	—	✓
22	—	✓	—
25	—	—	✓
28	—	✓	—
30	—	—	✓
35	—	✓	—
38	—	—	✓
42	—	✓	—

The chart clearly shows the different size progression used by the L and S series.

DIN 2353 L-Series Tube Sizes

The standard metric OD sequence commonly used for L-series fittings is:

6 – 8 – 10 – 12 – 15 – 18 – 22 – 28 – 35 – 42 mm

For example, common tube specifications may be written as:

• 6 × 1 mm
• 8 × 1 mm
• 10 × 1 mm
• 12 × 1.5 mm
• 15 × 1.5 mm
• 18 × 2 mm
• 22 × 2 mm
• 28 × 2.5 mm
• 35 × 3 mm
• 42 × 3 mm

The first value identifies the tube OD, while the second identifies the tube wall thickness.

DIN 2353 S-Series Tube Sizes

The standard OD progression commonly associated with S-series fittings is:

6 – 8 – 10 – 12 – 14 – 16 – 20 – 25 – 30 – 38 mm

Example tube specifications include:

• 6 × 1.5 mm
• 8 × 1.5 mm
• 10 × 1.5 mm
• 12 × 2 mm
• 14 × 2 mm
• 16 × 2 mm
• 20 × 2.5 mm
• 25 × 3 mm
• 30 × 4 mm
• 38 × 5 mm

These examples illustrate typical ways metric hydraulic tubing may be specified; the required wall thickness must ultimately be selected according to the tube material, system pressure, temperature, applicable design standard, fitting manufacturer’s requirements, and required safety factor.

How to Read the Tube Size

Consider the designation:

20 × 2.5 mm

It means:

Tube OD = 20 mm

Wall thickness = 2.5 mm

The corresponding inside diameter is:

ID = 20 − (2 × 2.5)

ID = 15 mm

Therefore:

Parameter	Dimension
Outside Diameter	20 mm
Wall Thickness	2.5 mm
Inside Diameter	15 mm

The 20 mm OD determines the basic DIN 2353 fitting size, while the wall thickness influences tube strength, flow area, assembly requirements, and pressure capability.

For actual system design, the tube OD chart should therefore be used together with the manufacturer’s pressure-rating and approved tube wall-thickness tables, rather than selecting tubing based on OD alone.

5. DIN 2353 L-Series Tube Size Chart

The L Series (Light Series) is one of the most commonly used DIN 2353 fitting series. It is designed for general hydraulic and industrial applications where a compact connection with good pressure capability is required.

The standard tube OD progression commonly associated with the L series is:

6 – 8 – 10 – 12 – 15 – 18 – 22 – 28 – 35 – 42 mm

DIN 2353 L-Series Size Chart

Tube OD (mm)	Typical Tube Size Example (OD × Wall)	Calculated ID (mm)
6	6 × 1.0	4.0
8	8 × 1.0	6.0
10	10 × 1.0	8.0
12	12 × 1.5	9.0
15	15 × 1.5	12.0
18	18 × 2.0	14.0
22	22 × 2.0	18.0
28	28 × 2.5	23.0
35	35 × 3.0	29.0
42	42 × 3.0	36.0

The wall thicknesses shown above are representative examples, not universal requirements. A given tube OD can often be supplied with several different wall thicknesses.

For example, a 12 mm OD tube might be available as:

• 12 × 1.0 mm
• 12 × 1.5 mm
• 12 × 2.0 mm

Although all three have the same outside diameter, their inside diameters and pressure capabilities are different.

Where Is the L Series Used?

DIN 2353 L-series fittings are commonly found in:

• Industrial hydraulic power units
• Machine tools
• Lubrication systems
• Agricultural machinery
• Mobile hydraulic equipment
• General manufacturing equipment
• Marine auxiliary systems
• Industrial fluid lines

The L series is often selected when the application does not require the heavier construction of an S-series fitting.

However, the designation “Light Series” does not mean low-pressure tubing. Depending on the fitting size, material, tube specification, and manufacturer, L-series fittings can be used in relatively high-pressure hydraulic applications.

Selecting L-Series Tubing

When selecting tubing for an L-series fitting, engineers should verify at least four parameters:

Tube OD + Wall Thickness + Tube Material + System Design Pressure

For example:

18 × 2 mm, stainless steel tube

does not necessarily have the same allowable working pressure as:

18 × 2 mm, carbon steel tube

even though their nominal dimensions are identical.

The fitting manufacturer’s tubing requirements should therefore be checked before specifying the final tube size.

---

6. DIN 2353 S-Series Tube Size Chart

The S Series (Heavy Series) is designed for more demanding hydraulic applications where higher mechanical strength and pressure capability are required.

The commonly recognized S-series tube OD sequence is:

6 – 8 – 10 – 12 – 14 – 16 – 20 – 25 – 30 – 38 mm

Notice that this progression differs from the L series, particularly at larger sizes.

DIN 2353 S-Series Size Chart

Tube OD (mm)	Typical Tube Size Example (OD × Wall)	Calculated ID (mm)
6	6 × 1.5	3.0
8	8 × 1.5	5.0
10	10 × 1.5	7.0
12	12 × 2.0	8.0
14	14 × 2.0	10.0
16	16 × 2.0	12.0
20	20 × 2.5	15.0
25	25 × 3.0	19.0
30	30 × 4.0	22.0
38	38 × 5.0	28.0

Again, the wall thicknesses in this table are examples only. The actual allowable tube dimensions depend on the tube material, fitting design, operating pressure, temperature, and manufacturer requirements.

S Series vs. L Series

The difference between L and S is not simply tube wall thickness.

They are different fitting series with different dimensional characteristics.

Feature	L Series	S Series
Designation	Light	Heavy
Typical Service	General hydraulic	Heavy-duty hydraulic
Construction	Lighter	More robust
Typical Pressure Capability	Moderate to high	Generally higher
Size Sequence	6–42 mm	6–38 mm
Large OD Examples	22, 28, 35, 42 mm	20, 25, 30, 38 mm

For example, an 18 mm L-series fitting cannot simply be replaced with an S-series fitting of the same nominal designation, because 18 mm is not part of the common S-series tube OD progression.

Likewise:

• 22 mm is a common L-series size.
• 20 mm is a common S-series size.
• 28 mm is a common L-series size.
• 25 mm is a common S-series size.
• 35 mm is a common L-series size.
• 30 mm is a common S-series size.

This is one reason why identifying the fitting series is essential before ordering replacement components.

Typical S-Series Applications

S-series DIN 2353 fittings are frequently used in:

• Hydraulic presses
• Heavy construction machinery
• Mining equipment
• Mobile hydraulic systems
• High-pressure power units
• Marine hydraulic systems
• Steel production machinery
• Heavy manufacturing equipment

Where pressure pulsation, vibration, shock loading, or high mechanical loads are present, the S series may be preferred when permitted by the system design.

The final selection should always be based on the required pressure rating and manufacturer’s technical data rather than selecting S series simply because it is described as “heavy.”

---

7. DIN 2353 Tube OD and Wall Thickness

A DIN 2353 tube connection cannot be selected correctly using outside diameter alone. Tube wall thickness is another critical parameter because it influences pressure capability, internal flow area, mechanical strength, and fitting assembly.

Metric hydraulic tubing is normally written as:

OD × Wall Thickness

For example:

16 × 2 mm

means:

• Outside diameter = 16 mm
• Wall thickness = 2 mm

The inside diameter can then be calculated as:

ID = OD − 2t

where:

• ID = tube inside diameter
• OD = tube outside diameter
• t = tube wall thickness

For a 16 × 2 mm tube:

ID = 16 − (2 × 2)

ID = 12 mm

Effect of Wall Thickness on Tube ID

Consider three tubes having the same 16 mm outside diameter:

Tube Size	OD (mm)	Wall (mm)	ID (mm)
16 × 1.0	16	1.0	14
16 × 1.5	16	1.5	13
16 × 2.0	16	2.0	12
16 × 2.5	16	2.5	11
16 × 3.0	16	3.0	10

Increasing the wall thickness decreases the internal diameter even though the fitting still connects to a 16 mm OD tube.

This has two important consequences.

First, a thicker wall generally allows the tube to withstand greater internal pressure, assuming the same material and other design conditions.

Second, the smaller ID reduces the available flow area and can increase fluid velocity and pressure loss.

Tube Flow Area

The internal cross-sectional flow area can be calculated using:

A = π × ID² / 4

For a 16 × 2 mm tube:

ID = 12 mm

Therefore:

A = π × 12² / 4

A ≈ 113.1 mm²

Now compare it with a 16 × 3 mm tube:

ID = 10 mm

A = π × 10² / 4

A ≈ 78.5 mm²

Although both tubes have the same 16 mm OD, the 16 × 3 mm tube has substantially less internal flow area.

This demonstrates why tube sizing should consider both pressure capability and hydraulic flow requirements.

Wall Thickness and Pressure Capability

For a given tube material and OD, increasing the wall thickness generally increases the tube’s resistance to internal pressure.

However, the allowable working pressure should not be determined from wall thickness alone.

Other factors include:

• Tube material
• Material strength
• Tube manufacturing specification
• Temperature
• Corrosion allowance
• Pressure cycling
• Vibration
• Tube tolerances
• Fitting design
• Safety or design factor

The allowable pressure of the complete connection may also be limited by the fitting rather than the tubing.

Therefore:

System Working Pressure ≤ Lowest Rated Component

If the tube is rated for a higher pressure than the fitting, the fitting rating becomes the limiting factor.

Common DIN 2353 Tube Size Examples

Metric hydraulic tubes used with DIN-style fittings are commonly specified in formats such as:

Tube Designation	OD	Wall	ID
6 × 1	6 mm	1 mm	4 mm
8 × 1	8 mm	1 mm	6 mm
10 × 1.5	10 mm	1.5 mm	7 mm
12 × 1.5	12 mm	1.5 mm	9 mm
16 × 2	16 mm	2 mm	12 mm
20 × 2.5	20 mm	2.5 mm	15 mm
25 × 3	25 mm	3 mm	19 mm
30 × 4	30 mm	4 mm	22 mm
38 × 5	38 mm	5 mm	28 mm

These values illustrate how DIN metric tube dimensions are specified, but they should not be treated as a universal wall-thickness recommendation.

For an actual hydraulic system, the correct approach is to first determine the required flow rate and design pressure, select an appropriate tube OD and wall thickness, and then verify that the selected tubing is compatible with the required DIN 2353 fitting series and manufacturer’s pressure-rating data.

8. DIN 2353 Tube Size vs. Inch Tube Size

DIN 2353 fittings are primarily designed around metric tube outside diameters, while many North American tubing systems use fractional-inch outside diameters. Although some metric and inch sizes appear very close, they should not be considered directly interchangeable.

For example:

• 6 mm = approximately 0.236 in
• 12 mm = approximately 0.472 in
• 25 mm = approximately 0.984 in

These values are close to certain fractional-inch dimensions but are not necessarily the same actual OD.

Metric to Inch Tube Size Comparison

The conversion between millimeters and inches is:

1 inch = 25.4 mm

Therefore:

Inches = Millimeters ÷ 25.4

The following table provides useful dimensional comparisons.

Metric Tube OD	Exact Inch Equivalent	Nearby Common Inch OD
6 mm	0.236 in	1/4 in (0.250)
8 mm	0.315 in	5/16 in (0.3125)
10 mm	0.394 in	3/8 in (0.375)
12 mm	0.472 in	1/2 in (0.500)
14 mm	0.551 in	9/16 in (0.5625)
15 mm	0.591 in	5/8 in (0.625)
16 mm	0.630 in	5/8 in (0.625)
18 mm	0.709 in	3/4 in (0.750)
20 mm	0.787 in	3/4 in (0.750)
22 mm	0.866 in	7/8 in (0.875)
25 mm	0.984 in	1 in (1.000)
28 mm	1.102 in	1-1/8 in (1.125)
30 mm	1.181 in	1-3/16 in (1.1875)
35 mm	1.378 in	1-3/8 in (1.375)
38 mm	1.496 in	1-1/2 in (1.500)
42 mm	1.654 in	1-5/8 in (1.625)

The table is useful for dimensional reference, but the “nearby” inch size is not a recommended substitute for the metric tube.

Why Metric and Inch Tubes Are Not Automatically Interchangeable

Consider a DIN fitting designed for a 12 mm tube.

A 1/2-inch tube has an actual OD of:

1/2 in × 25.4 = 12.70 mm

The difference is:

12.70 − 12.00 = 0.70 mm

That difference is significant for a compression fitting designed to grip and seal against the tube OD.

Likewise, 1/4-inch tubing has an OD of 6.35 mm rather than 6.00 mm.

Installing an incorrect tube OD can affect:

• Cutting-ring engagement
• Sealing
• Tube support
• Assembly travel
• Mechanical retention
• Pressure capability

DIN 2353 fittings should therefore be matched to the tube OD specified by the fitting manufacturer.

Metric and Inch Adapters

When a system needs to transition between DIN metric tubing and an inch-based tubing system, a purpose-designed adapter should normally be used.

For example:

12 mm DIN Connection → Adapter → 1/2 in Tube Connection

This allows each side of the adapter to properly match its respective tubing system rather than attempting to install a nearly equivalent tube into an incompatible fitting.

---

9. How to Select the Correct DIN 2353 Tube Size

Selecting the correct DIN 2353 tube size involves more than choosing a tube that physically fits the connector. The tubing must provide sufficient flow capacity, pressure capability, mechanical strength, and compatibility with the fitting system.

A practical selection process is outlined below.

Determine the Required Flow Rate

The first consideration is the required fluid flow.

The tube ID must provide enough internal area to maintain an acceptable fluid velocity.

Fluid velocity can be estimated from:

v = Q / A

where:

• v = fluid velocity
• Q = volumetric flow rate
• A = internal flow area

The tube flow area is:

A = π × ID² / 4

A tube that is too small increases fluid velocity and can contribute to:

• Higher pressure drop
• Increased heat generation
• Higher energy losses
• Noise
• Increased turbulence

For this reason, tube OD should not be selected based only on fitting availability.

Determine the System Design Pressure

Next, determine the maximum pressure that the tube assembly may experience.

Consider:

• Normal working pressure
• Maximum operating pressure
• Pressure spikes
• Pressure pulsation
• Temperature
• Required design or safety factors

The selected tube and fitting assembly must have adequate pressure capability for the application.

Select Tube OD

Once the required flow capacity has been established, an appropriate tube OD can be selected.

For example, the common L-series sequence is:

6 – 8 – 10 – 12 – 15 – 18 – 22 – 28 – 35 – 42 mm

The common S-series sequence is:

6 – 8 – 10 – 12 – 14 – 16 – 20 – 25 – 30 – 38 mm

The correct size depends on both the hydraulic requirements and the fitting series.

Select the Tube Wall Thickness

After choosing the OD, select an appropriate wall thickness.

For example, a 12 mm tube might be specified as:

• 12 × 1.0 mm
• 12 × 1.5 mm
• 12 × 2.0 mm

Their calculated IDs are:

Tube Size	ID
12 × 1.0 mm	10 mm
12 × 1.5 mm	9 mm
12 × 2.0 mm	8 mm

Increasing wall thickness generally improves pressure capability but reduces internal flow area.

The wall thickness must also be suitable for the fitting assembly method. Depending on the tube material, OD, wall thickness, and fitting design, a manufacturer may specify additional tube-support or assembly requirements.

Select L or S Series

The fitting series must then be selected according to the system requirements.

As a general distinction:

L Series → General hydraulic and industrial service

S Series → More demanding and higher-pressure hydraulic service

However, S series should not automatically be selected whenever pressure is high. The actual allowable working pressure of the specific fitting size and configuration must be checked.

Check Tube Material

Common tubing materials used with DIN-style fittings include:

• Carbon steel
• Stainless steel
• Other compatible metallic tubing specified by the fitting manufacturer

Material selection depends on:

• Fluid compatibility
• External environment
• Corrosion resistance
• Temperature
• Mechanical properties
• Pressure requirements

Stainless steel, for example, is commonly selected where corrosion resistance is important.

Verify Tube Tolerances and Surface Condition

Compression fittings depend on controlled tube dimensions and surface quality.

Before assembly, check that the tube is:

• Within specified OD tolerance
• Round and undamaged
• Free from deep scratches
• Properly cut
• Correctly deburred
• Clean
• Compatible with the fitting material and design

A deep longitudinal scratch across the sealing or gripping area can compromise connection performance.

Verify the Complete Assembly Rating

The final system rating should be based on the lowest-rated component in the assembly.

For example, a tube may have an allowable pressure greater than the connected fitting. In this situation, the fitting determines the maximum permissible system pressure.

Always verify:

Tube + Fitting + Adapter + Valve + Hose + Other Components

against the system design conditions.

Manufacturer technical data should be used for final engineering selection.

---

Conclusion

The DIN 2353 tube size system provides a standardized approach for connecting metric tubing in hydraulic and industrial fluid systems. Its 24° cone connection design has become widely used because it provides a compact, mechanically secure, and serviceable tube connection.

DIN 2353 fittings are primarily selected according to the actual metric tube outside diameter.

The commonly encountered fitting series are:

• LL – Extra Light Series
• L – Light Series
• S – Heavy Series

For L-series fittings, common tube ODs include:

6, 8, 10, 12, 15, 18, 22, 28, 35 and 42 mm

For S-series fittings, common tube ODs include:

6, 8, 10, 12, 14, 16, 20, 25, 30 and 38 mm

Tube OD alone, however, is not sufficient for engineering selection. The wall thickness, ID, material, pressure rating, temperature, flow requirements, tube tolerances, and fitting series must all be considered.

A tube specification such as:

16 × 2 mm

means a 16 mm outside diameter with a 2 mm wall thickness, producing a calculated 12 mm inside diameter.

Finally, metric DIN tubing should not be replaced with a nearby fractional-inch tube simply because the dimensions appear similar. DIN 2353 compression connections depend on controlled tube dimensions, and even relatively small OD differences can affect assembly, gripping, sealing, and pressure performance.

For critical or high-pressure applications, always verify the final tube and fitting combination against the current applicable DIN/ISO requirements and the fitting manufacturer’s technical documentation before installation.

Hydraulic Oil Compatibility Chart

Pressure Drop Calculator: Formula, Examples & Guide