10311 Metric Male Flat-Seal O-Ring Hydraulic Hose Fittings

Metric flat-seal hydraulic hose fittings seal on a flat face with an O-ring instead of a taper thread or a 24-degree cone, which makes them the standard connection on many Chinese and Asian hydraulic machines. The 10311 series covers 17 part numbers from DN6 (-04) to DN50 (-32) with metric fine threads from M12x1.25 to M64x2, engineered for wire-braided hydraulic hose. If you build, repair or source hose assemblies for metric flat-face O-ring ports, this page gives you the full reference: dimensions, part numbers, assembly rules and OEM options.

Why Choose These Metric Flat-Seal Fittings

• Leak-tight O-ring flat-face seal. The O-ring is compressed between two flat faces, so the joint stays sealed under pressure spikes, shock and vibration. No thread sealant, no tape, easy to assemble and re-torque.
• 17 sizes from DN6 to DN50. Metric fine threads from M12x1.25 to M64x2 cover everything from small control lines to large return lines.
• Built for wire-braided hose. Use the 10311 series with braided hose; the 10312 series covers the same thread range for spiral hose.
• OEM-ready. Laser marking with your logo and batch number, custom plating, material test reports and batch traceability for every order.

Standards and traceability. Threads are ISO 724 metric fine threads. The sealing geometry follows the flat-face O-ring configuration used across the widely adopted Chinese 10-series hose fitting numbering system. Fittings are designed to pair with wire-braided hose built to EN 853 1SN/2SN or SAE 100 R1AT/R2AT performance classes. Dimensional inspection reports and material test certificates are available for OEM gate checks.

What Is a Metric Flat-Seal Fitting and How Does the O-Ring Seal Work?

A metric flat-seal hose fitting has a straight metric male thread on the port end and a flat sealing face. The thread is parallel, which means the thread itself does not seal anything. Sealing happens when the O-ring is compressed between the flat face of the stud and the flat seat of the female port as the nut is torqued. One sentence to remember: the O-ring does the sealing, and the thread only holds the joint together.

That is why you must never wrap PTFE tape on a flat-seal metric male thread. Tape belongs on taper threads such as NPT or BSPT. On a straight-thread O-ring joint, tape adds nothing and can push into the system when the fitting is tightened.

10311 flat-seal vs DIN 2353 (24-degree cone): do not interchange

Both families use metric threads, but the sealing geometry is different. DIN 2353 / ISO 8434-1 style fittings seal on a 24-degree cone, while the 10311 series seals on a flat face with an O-ring. Even if the thread size looks the same, the two will not seal together. Check the sealing face before ordering: cone face means cone-series fittings, flat face with an O-ring groove or loose O-ring means flat-seal series fittings.

10311 flat-seal vs SAE ORFS

SAE ORFS (O-ring face seal) also seals on a flat face with an O-ring, but it uses inch UN/UNF threads. The 10311 series uses metric fine threads. The two are not interchangeable and should never be mixed in one joint.

Straight-thread O-ring vs taper thread (NPT/BSPT)

10311 Series Technical Specifications

Materials and processing

• Body material options: high-strength carbon steel (20#/35#/45# grades, cold-formed or machined) as standard; stainless steel 304 or 316L available for corrosive or wash-down environments.
• Surface treatment: zinc plating as standard; yellow, white or black zinc, zinc-nickel and Dacromet coating available for higher salt-spray requirements.
• Heat treatment: hardness and case depth are controlled per drawing to keep the thread and the barb zone fatigue-resistant; typical surface hardness range HRC 20-28 (confirm the exact code on your drawing or PO).
• O-ring seal: NBR as standard for mineral oils from about -30°C to +100°C continuous; FKM (Viton-type) available for higher temperatures and aggressive fluids. O-ring size and material are confirmed per part number at order time.

Full dimension and part number table

All linear dimensions are in millimeters. E = thread, DN = hose bore, A and C = lengths per the supplier drawing, S1 = hex across flats.

Full dimensioned CAD drawings are available on request so your engineers can verify every length before you commit a batch.

Working pressure: the honest answer engineers need

A crimp hose assembly fails at its weakest link, so the rating of a 10311 fitting depends on the hose you pair it with and the crimp quality. Wire-braided hydraulic hose in this size range typically operates between roughly 80 and 400 bar depending on bore size and construction (1SN or 2SN). Send us your hose specification and we will confirm the working pressure, burst margin and the recommended ferrule for your exact hose brand – the check is free and takes one message. For derating at elevated temperature, always follow the hose manufacturer’s pressure-temperature curve, since the rubber cover and tube lose capacity above about +100°C.

Which Fitting Series Do You Need: 10311 (Braided) or 10312 (Spiral)?

The part number changes with the hose construction, because the barb geometry and the crimp parameters are different. This is the first selection check for every order.

When in doubt, check the hose label: braided hose is marked 1SN, 2SN or R1AT, R2AT; spiral hose is marked 4SP, 4SH or similar. Ordering the wrong series means the ferrule will not crimp correctly, so confirm the hose construction before you buy.

Part Number Decoder and How to Order

The 10311 part number carries the whole specification, so purchasing can copy it straight into a PO without another round of emails:

10311 – 22 – 08

• 10311 = flat-seal fitting series for braided hose
• 22 = thread nominal size (here M22x1.5)
• 08 = hose dash size (here DN12, 1/2-inch class bore)

Because one thread size can serve several hose bores, always quote both the thread size and the dash size. For example, M16x1.5 is available as 10311-16-04, 10311-16-05 and 10311-16-06. If you are replacing an existing fitting, send us a photo of the thread side and the hose side, plus the hex size, and we will confirm the matching part number the same day. This service is the fastest way to convert an unreadable old part number into a confirmed 10311 order number.

Each 10311 fitting is supplied with the matched O-ring or with the O-ring specified for your port configuration. If your assembly loses an O-ring during maintenance, replacement O-rings are available separately, so you never scrap a fitting because of a lost seal.

Assembly Guide: Four Steps to a Reliable Crimp

These fittings are crimp-style hose ends: the barbed tail is pushed into the hose and a matching ferrule is crimped over the cover. Follow the four steps below on every assembly.

Step 1 – Cut the hose square. Use a sharp hose cutter or cutoff saw. A square, clean cut lets the ferrule grip the cover evenly. A beveled or ragged cut is the most common cause of pull-out failures.

Step 2 – Prepare the insert depth. Push the fitting tail into the hose until it bottoms firmly against the internal shoulder. The hose end must sit at the full insertion depth, not short, or the crimp zone will be wrong.

Step 3 – Lubricate and insert. Apply a thin film of assembly lubricant to the hose bore and the barb. Push the fitting in with a steady twisting motion until it bottoms out, then wipe away excess lubricant. Do not use grease on the sealing faces or the O-ring.

Step 4 – Crimp and verify. Crimp the matched ferrule with the hose manufacturer’s crimp specification. After crimping, always measure the crimp outside diameter with a caliper and compare it with the crimp table. The measured value must sit inside the allowed tolerance band. If it is out of tolerance, do not put the assembly into service – cut it off and re-crimp with a corrected setting.

Warnings: three mistakes that cause leaks and blow-outs

• Never mix hoses, fittings and ferrules from different manufacturers. Even when the dash size matches, crimp parameters and barb geometry differ, and a mismatched set can leak or pull apart under pressure.
• Never put PTFE tape or sealant on a straight metric thread. The 10311 seals with its O-ring. Tape belongs only on taper threads such as NPT or BSPT. Mixing up straight-thread O-ring sealing and taper-thread sealing is the number one field error on metric flat-seal joints.
• Never force a 24-degree cone fitting or an ORFS fitting onto a flat-seal port because the threads happen to fit. The seal face will not mate, and the joint will leak or damage the port.

Typical Applications

Metric flat-face O-ring ports are specified across a wide range of hydraulic equipment, especially machines built to Chinese or Asian standards and their global service networks:

• Hydraulic power units, presses and machine tools
• Plastic injection and die-casting machinery
• Mining, tunneling and construction equipment
• Agricultural and forestry machinery
• Material handling and mobile equipment
• Marine and offshore auxiliary systems

Wherever the port face is flat and carries an O-ring groove, the 10311 series is the direct hose connection for braided hose circuits.

OEM Customization and Quality Traceability

For equipment builders and large maintenance programs, the 10311 series can be adapted to your exact drawing and your traceability rules.

Customization options

• Thread and geometry: special threads, modified lengths and non-standard barb configurations machined to your drawing or to a sample.
• Surface treatment: zinc-nickel, Dacromet or other coatings for higher salt-spray grades; we confirm the achieved test hours for the coating you choose instead of quoting a generic number.
• Laser marking: your logo, part number and batch or date code laser-marked on the hex for full field traceability.
• Material: stainless steel 304/316L versions for corrosive media or wash-down duty.
• Packaging and kitting: custom labels, barcodes, poly-bag or box quantities, and complete hose assembly kitting if you want ready-to-install assemblies.

Quality documentation

• Batch number traceability: every order carries a batch code that links back to the production records.
• Material test reports (MTR) available for carbon steel and stainless batches.
• Dimensional inspection reports for OEM gate checks.
• Third-party inspection (BV, SGS or similar) can be arranged before shipment.

Samples and MOQ. Samples for stock sizes ship fast, and we keep low MOQs for standard part numbers so distributors can test the series without tying up capital. OEM programs can move to scheduled deliveries once the drawing is approved.

Packaging and Logistics

Standard export packing: fittings are individually poly-bagged or boxed to protect threads and O-rings, then packed in export cartons labeled with part number, quantity and batch code. Custom labeling, kitting and barcode requirements are available for distributors and OEMs. Exact carton quantity, gross weight and CBM are confirmed on the packing list for every order so you can calculate freight before you commit.

FAQ

Q: What is a metric flat-seal hydraulic hose fitting? A: It is a crimp-style hose fitting with a straight metric male thread and a flat sealing face. It seals by compressing an O-ring between the flat face of the stud and the flat seat of the female port, so no thread sealant is needed.

Q: What is the difference between 10311 and 10312 series? A: 10311 is for wire-braided hose (1SN/2SN or R1AT/R2AT) and 10312 is for spiral hose (4SP/4SH style). The thread range is the same, but the barb geometry and crimp parameters differ.

Q: Is this fitting the same as a DIN 2353 or ORFS fitting? A: No. DIN 2353 style fittings seal on a 24-degree cone, and SAE ORFS uses inch threads. This series uses metric threads and seals on a flat face with an O-ring. The three families are not interchangeable.

Q: Do I need thread tape or sealant on the male thread? A: No. The O-ring does the sealing. Tape on a straight metric thread is useless and can contaminate the system. Use tape only on taper threads.

Q: Which hose can I use with a 10311 fitting? A: Wire-braided hydraulic hose in the matching dash size, typically 1SN or 2SN. For spiral hose, use the 10312 series.

Q: What is the working pressure of these fittings? A: The assembly rating depends on the hose, the ferrule and the crimp quality. Send your hose specification and we will confirm the working pressure and the recommended ferrule for your combination.

Q: What temperature range does the seal handle? A: With the standard NBR O-ring, roughly -30°C to +100°C continuous. FKM seals extend the range for hot oil and aggressive fluids. The hose itself sets the system limit.

Q: Can you make custom part numbers with my logo? A: Yes. We offer laser marking, custom plating, stainless versions and special dimensions, with MTR and batch traceability for OEM programs.

Order Today: Metric Flat-Seal Hydraulic Hose Fittings with Confirmed Fit

Every 10311 metric flat-seal hydraulic hose fitting in this range is made to controlled dimensions, inspected before packing and backed by batch traceability. Send us your hose type, thread size and dash size – or just a photo of the old fitting – and you will get a confirmed part number, a delivery date and a quote within one working day. Request samples first if you want to test the fit on your own bench. The O-ring does the sealing, and we do the confirming: tell us your application, and we will make sure the fitting, ferrule and hose work as one leak-free assembly.