Metric Fittings

What Are Metric Hydraulic Fittings?

A metric fitting is a type of connector specifically designed for piping systems utilizing metric dimensions; both its threads and dimensional specifications adhere to the metric unit system. Based on metric units, its thread specifications—such as M-series threads—enjoy a high degree of universality and standardization globally, particularly in European nations and countries such as China and Japan, where the metric system is adopted.

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These metric hydraulic fittings serve as critical components for connecting hydraulic hoses and rigid tubing to elements such as hydraulic cylinders, hydraulic pumps and valves; utilizing standardized threads, they enable rapid assembly with plugs or adapters and are available in a wide variety of geometries and specifications to accommodate the diverse connection requirements of hydraulic systems, ensuring the safe, stable, and leak-free transmission of hydraulic oil under high-pressure conditions.

Strongflex specializes in manufacturing hydraulic connection products, offering a wide range of metric hydraulic fose fittings. Our products conform to international standards such as DIN and ISO, and can meet the needs of various fields including construction machinery, agricultural machinery, mining equipment, and industrial hydraulic systems.

Metric Hose Fittings

Metric Fitting Standards

DIN Standard (represented by DIN 2353): This is the most prevalent standard globally for compression fittings, holding a dominant position particularly within the European and Chinese markets. It achieves a seal through the mechanical bite of a ferrule onto the tubing; as it requires no O-rings, it offers high reliability. This standard is subdivided into three series—LL (Extra-Light), L (Light), and S (Heavy)—to accommodate various pressure ratings.

JIS Standard: Commonly found in Japanese and Korean equipment, such as excavators manufactured by brands like Komatsu, Hitachi, and Kobelco. Its defining characteristic is the use of a 30° or 60° flared cone surface to achieve the seal.

ISO Standard: This can be regarded as a globally harmonized standard. For instance, ISO 8434-1 is interchangeable with the DIN 2353 standard, while ISO 6149 defines metric port threads that utilize O-ring seals.

Metric hose fittings Sealing Principle & Design

Metric hydraulic hose fittings mainly rely on metal-to-metal sealing or O-ring sealing, depending on the type:

• 24° Cone Seal: Creates a tight seal through cone-to-cone contact
• DKO (O-ring Seal): Provides additional sealing reliability under high pressure
• Light vs Heavy Series:
  a. Light Series (L): Medium pressure applications

• b. Heavy Series (S): High pressure systems

Understanding the sealing type is critical to avoid leakage and ensure compatibility.

Metric Hydraulic Fittings Product Types

Some common types of metric threads found in hydraulic fittings include:

• Metric Flat Face Fittings
• Metric Multiseal Fittings
• Metric 24° Cone Seal (subdivided into Light Series [L Series / DKOL], Heavy Series [S Series / DKOS], and Optional O-ring Sealing)
• Metric 24° Multiseal (also subdivided into Light and Heavy Series)
• Metric 60° Cone Seal Fittings
• Metric 74° Cone Seal Fittings
• Metric 90° Cone Seal Fittings
• Metric Standpipe (Straight)
• Metric Banjo Fittings
• Komatsu 30° Flare Metric Fittings: These are metric threads unique to Komatsu machinery, differing slightly from standard metric threads.

Applications of Metric Hose Fittings

Metric hose fittings are the most widely used type of connector in industrial sectors worldwide, particularly within hydraulic and pneumatic systems.

Industrial Manufacturing: Hydraulic and lubrication systems for equipment such as machine tools, molds, and metallurgical machinery.

Mechanical Equipment: Power output systems for engineering machinery—including excavators, loaders, and tractors—as well as agricultural machinery.

Energy Facilities: Reinforcement and structural support for petrochemical plants and natural gas pipelines.

Automation and Precision Equipment: Applications in automotive manufacturing, electronics assembly, food processing, and medical equipment. Due to their compact installation footprint, metric fittings are ideally suited for high-frequency operations and precision control requirements.

Automotive Industry: Thanks to their lightweight nature and compact design, metric fittings are extensively utilized in automotive power, braking, cooling, and fuel systems.

How to Measure Metric Hydraulic Fittings?

First, determine whether the fitting features external threads or internal threads. If it has external threads, use a caliper to measure the diameter at the outermost edge of the threads. Be careful not to take measurements at the thread run-out or chamfered sections. Record the value; for example, if the measured value is 13.8 mm (approximately 14 mm), it corresponds to an M14 size.

If the fitting has internal threads, use the caliper jaws to measure the inner diameter at the root (solid base) of the threads. This value is approximately equal to the thread’s major diameter minus one pitch. For instance, if the measured value is 12.5 mm, it typically corresponds to an M14 size.

When testing fittings, you may also encounter tapered threads versus parallel threads. For parallel threads, simply measure the diameter directly at the outermost edge. For tapered threads, measure the outer diameter at the third full thread from the end.

Next, measure the thread pitch—the distance between the crests (peaks) of adjacent threads—expressed in millimeters. Use a thread pitch gauge to test against the threads; find the gauge blade that fits perfectly into the threads, and read the corresponding value. The measurement method is the same for both internal and external threads.

Measure Metric Fittings Thread Pitch

Finally, determine the full specification by combining the two values: M + Nominal Diameter × Pitch (e.g., M14 × 1.5).

How to Identify Metric Fittings?

Identify the Thread Type: Metric threads feature a 60° equilateral profile. First, determine whether the threads are parallel or tapered. Parallel threads (typically designated with an “M”) require an O-ring or gasket to achieve a face seal, whereas tapered threads rely on the compressive interference of the threads themselves to create a seal.

Measure Key Dimensions: Use a caliper to precisely measure the thread’s outer diameter and pitch (the distance between two adjacent thread crests). This is the most direct method for determining the thread specification (e.g., M8 × 1.0).

How Do I Choose the Right Metric Hydraulic Fittings for My Application?

1. Determine System Pressure
Identify the system’s maximum working pressure to determine the appropriate fitting series. You should consider the pressure and flow requirements, as these determine the size and type of hydraulic hoses, tubing, or piping you will use.

2. Identify Fittings Type
Measure and verify the thread specifications (e.g., M14×1.5) and sealing mechanism of the equipment port (e.g., 24° cone, O-ring face seal, or requiring a bonded seal). This is crucial to avoid purchasing the wrong parts.

3. Determine Tubing Dimensions
Measure the outer diameter and wall thickness of the hose or rigid tubing. Note: Compression fittings (ferrule fittings) must precisely match the outer diameter of the rigid tubing.

4. Consider Material and Environment
For standard mineral oil systems, zinc-plated carbon steel is sufficient; however, for corrosive environments—such as damp, outdoor, or chemical settings—stainless steel should be selected.

5. Select Fitting Configuration
Choose the appropriate geometric shape based on the tubing layout and available space: straight, 45° elbow, 90° elbow, or a 360° swivel fitting, among others.

FAQ about Metric hydraulic hose fittings

What are the advantages of using metric fittings?

The primary advantage of using metric hydraulic fittings is their strong global interchangeability, which facilitates the purchasing or replacement of components. Secondly, metric hydraulic fittings offer excellent sealing performance; they are vibration-resistant, resistant to loosening, capable of withstanding high pressures (up to 630–700 bar), and present a low risk of leakage. They are also easy to install and offer high cost-effectiveness.

Can Metric and Imperial Hydraulic Fittings Be Mixed?

They cannot be mixed directly. Even if the threads appear similar, forcing them together will result in severe leakage or equipment damage, as their thread profiles do not match and their sealing principles differ.

What is the difference between DIN and Metric fittings?

DIN fittings refer to hydraulic fittings manufactured according to the German DIN standard, while “metric fittings” refer to fittings using metric threads. Many DIN hydraulic fittings use metric threads but are not directly interchangeable.

Are Metric fittings interchangeable with BSP fittings?

BSP and Metric connectors are not directly interchangeable. Their thread profile angle, pitch, and diameter standards are completely different. Forcing them together will result in stripping, leakage, or connection failure.

What pressure can Metric hydraulic fittings withstand?

The operating pressure depends on the type, material, size, and hydraulic hose assembly of the fitting. Standard stainless steel or carbon steel metric hydraulic fittings are commonly used in medium to high pressure hydraulic systems. For more product details, please contact us.

Can Metric fittings be customized?

Yes. Strongflex offers OEM and ODM customization services for metric hydraulic fittings, including custom thread sizes, materials, surface treatments, markings, and packaging. We can also manufacture fittings based on customer drawings or samples to meet specific application requirements.