Metric Thread with Captive Seal Adapter 2MC-WD / 2MD-WD (Metric Female 24° Cone Seat)

Why This Metric Thread with Captive Seal Adapter 2MC-WD / 2MD-WD Solves Two Ports at Once

The metric thread with captive seal adapter 2MC-WD / 2MD-WD is a straight adapter that joins a port machined with a plain metric male boss thread to a line terminated with a metric male 24° cone stud end. One side carries an outer metric thread with a captive seal, so the fitting seals on the flat face of the boss with a retained elastomer ring that cannot fall off during assembly. The other side is a metric female 24° cone seat that accepts the male 24° cone stud of a tube assembly and seals metal-to-metal on the 24° cone.

That combination is what makes this part useful. A machine that uses a captive-seal metric boss on the component side and DIN 3861 style 24° cone tube ends on the pipe side cannot be joined by a standard stud adapter, because the two families prepare their sealing surfaces differently. The metric thread with captive seal adapter 2MC-WD / 2MD-WD bridges exactly that gap with a single forged, single-piece body and two machined ends.

Two catalog series are covered here. The 2MC-WD series is the light L series, and the 2MD-WD series is the heavy S series. Both share the same design logic — captive seal on the male end, 24° cone seat on the female end — and differ in the wall thickness and the thread/stud proportions of the components they are designed to accept, which is why the S series is chosen when a heavier tube or a higher-pressure circuit is involved.

Core Advantages

1. Captive seal that cannot be dropped — the elastomer ring sits in the shoulder of the male end and is retained mechanically. There is no loose bonded washer to lose in a sump, no thread tape to wind and no sealant to cure.
2. Two interface families in one part — captive-seal metric boss on one side, metric female 24° cone seat on the other, so a single order line replaces a two-piece stack of adaptors.
3. Single-piece machined body — no brazed joints and no assembly threads inside the pressure envelope, so the only leak paths are the two designed sealing surfaces.
4. 24° cone seat is metal-to-metal reliable — the female cone seat on this adapter follows the metric 24° cone form used across DIN 3861 / ISO 8434-1 tube systems, so it mates with the standard male stud you already buy.
5. L series and S series in one drawing set — 2MC-WD covers light-duty circuits and 2MD-WD covers heavy-duty circuits, which keeps spare-part planning simple for machines that use both.
6. Batch traceability and free cross-reference — send an old part number, a drawing or a photograph and receive a written size recommendation within 24 hours.

Technical Specifications

What Is a Captive Seal Adapter?

A captive seal adapter is a straight fitting whose male end is threaded to a metric boss profile and sealed by an elastomer ring that is held on the fitting itself. The ring is compressed between the fitting shoulder and the flat face of the boss, so sealing is achieved at a face rather than in the thread. Because the seal is mechanically retained, the fitting can be carried, positioned and started by hand without the ring shifting or dropping.

The female end is a 24° cone seat. In this system the mating male stud has a 24° cone, and when the union nut is tightened the cone is pressed into the female seat and the two metal surfaces deform into contact. No elastomer is needed at that joint, which is why 24° cone connections tolerate high temperature and aggressive media better than many soft-seal joints.

The metric thread with captive seal adapter 2MC-WD / 2MD-WD therefore carries two entirely different sealing principles on one body. That is normal in hydraulic practice, and it is the reason the part exists.

Connection 1 — Metric Male Thread with Captive Seal

Connection 2 — Metric Female 24° Cone Seat

Dimensional Data

Full Part Number Matrix

The table above is transcribed in full from the 2MC-WD / 2MD-WD specification drawing: 10 light series L rows and 10 heavy series S rows, each carrying the stud thread E, the female 24° cone thread F, the tube outside diameter D1, the captive seal code, the dimensions A, L1, S1 and S2, and the pressure grade printed against that row. Order by the full PART NO. together with the seal code, because two rows can share a thread size and still require a different seal.

Materials and Finish

Working Pressure and Operating Envelope

Working pressure for the metric thread with captive seal adapter 2MC-WD / 2MD-WD is not a single number. It depends on the thread size, the boss material and wall thickness, the class of the mating port, and the temperature of the fluid. The light L series and the heavy S series exist precisely because two different pressure envelopes require two different amounts of metal around the same nominal thread. In general terms the L series is the choice for moderate-pressure control circuits and the S series is the choice where a heavier tube, a thicker wall or a higher circuit pressure is specified.

Request the size-specific pressure table with your enquiry and we will return the rating for the exact thread pair, the seal compound and the operating temperature you are running.

Why the Captive Seal Matters More Than It Looks

Every hydraulic leak has a cause, and one of the most common causes in the field is a seal that was never fitted correctly — a bonded washer that was dropped, a thread sealant that was applied to the wrong half of the joint, or an elastomer ring that rolled out of its groove while the fitter was reaching into a blind position.

The captive design removes that whole class of failure. The ring is on the fitting before it reaches the machine. It stays there while the fitting is carried, aligned and hand-started. It cannot be double-stacked, cannot be forgotten and cannot be substituted with a washer of the wrong thickness. For maintenance teams working on mobile equipment in a yard, or on skids where the boss faces downward, that is worth more than a small difference in unit price.

The 24° cone end contributes the second half of the reliability story. Metal-to-metal cone seals do not age, do not harden and are not affected by fluid compatibility in the same way as an elastomer. As long as the cone is undamaged and the union nut is tightened correctly, the joint is repeatable at reassembly. The combination of a captive elastomer face seal on one end and a 24° cone on the other therefore gives the assembly one soft seal where it is easy to inspect and one hard seal where the environment is harshest.

Installation Notes for the Metric Thread with Captive Seal Adapter 2MC-WD / 2MD-WD

1. Inspect both interfaces before assembly. Check the boss face for scratches and the 24° cone of the mating stud for dents or dirt. A face seal forgives very little grit.
2. Leave the captive seal in place. Do not remove the retained ring for cleaning and do not add a second washer. If the ring is damaged, replace the adapter’s seal — not the joint.
3. Hand-start the male end into the boss until the thread is fully engaged, then tighten to the torque value recommended for the thread size and the boss material.
4. Fit the tube assembly at the cone end and tighten the union nut by hand until the cone contacts the seat, then torque to the value specified for the stud and tube size.
5. Torque values are not interchangeable between the two ends. The captive seal end and the 24° cone end have different thread sizes and different sealing principles, so use the value that belongs to each interface.
6. Pressure-test after installation. Because the two ends seal by different mechanisms, a leak at one end tells you nothing about the other. Test the assembly as a whole before returning the machine to service.

Applications

The metric thread with captive seal adapter 2MC-WD / 2MD-WD is typically specified where a European-designed valve block, cylinder or pump uses a captive-seal metric boss and the machine builder wants to continue using a metric 24° cone tube system for the piping. Typical installations include:

• Mobile and agricultural machinery where circuits are assembled and serviced in the field
• Industrial power units and test stands built to mixed metric standards
• Injection moulding and press equipment with captive-seal manifold ports
• Machine tools where a compact straight transition is needed between two standards
• Replacement and repair work, where an existing adapter cannot be re-ordered and a functional equivalent is needed quickly

In all of these cases the driver is the same: two sealing systems have to meet, and the user wants one part, one torque step and one leak path to check.

Quality, Testing and Traceability

Every metric thread with captive seal adapter 2MC-WD / 2MD-WD is produced from controlled steel stock, and thread form, cone angle, seal groove and shoulder squareness are checked as part of the normal production flow. Assemblies are pressure tested, and batch labels allow a supplied adapter to be traced back to the material lot. Material test reports, dimensional inspection records and third-party inspection arrangements are available on request, and OEM laser marking of part numbers or customer references can be applied where the quantity supports it.

Ordering Information

To order, specify four things:

1. Series — light L (2MC-WD) or heavy S (2MD-WD)
2. Male thread size — the metric boss thread at the captive seal end
3. Female thread size — the metric 24° cone seat dimension at the other end
4. Seal compound — nitrile as standard, or an alternative elastomer for the fluid and temperature in service

If the two threads are the same size, the standard catalogue part number applies. If they differ, the adapter is made to order from the same body family.

FAQ

Can I replace a loose bonded washer with the metric thread with captive seal adapter 2MC-WD / 2MD-WD? No. The captive seal version is a different body. A bonded washer sits on a plain stud; a captive seal adapter has a machined groove and shoulder that retains the ring. Use the version that matches your port, or send us the drawing.

Is the 24° cone end the same as a 60° cone or BSP end? No. The 24° cone is the metric cone form used in DIN 3861 / ISO 8434-1 tube systems. A 60° cone or a tapered BSP thread is a different interface and will not seal correctly against it.

Which series should I choose, L or S? Match the series of the tube assembly and the port you are connecting. If the circuit is specified as light series L, use 2MC-WD; if it is specified as heavy series S, use 2MD-WD. Pressure and wall thickness requirements normally decide the question.

Can the adapter be used in both directions? The threads differ, so it is installed in the orientation shown in the drawing: captive seal end into the boss, 24° cone end to the tube assembly. It is not reversible.

Do you supply the mating stud and union nut? Yes. Tube assemblies, male 24° cone studs and union nuts can be supplied with the adapters so the joint arrives complete.

Request a Quote for the Metric Thread with Captive Seal Adapter 2MC-WD / 2MD-WD

Send us the port drawing, the mating stud part number or a photograph of the existing fitting and we will confirm the series, the thread pair, the seal compound and the lead time within 24 hours. Please include the working pressure, the fluid and the operating temperature so that we can quote the correct material and elastomer combination rather than a nominal equivalent. Spare seals, mating studs and complete tube assemblies are available on the same order.

Browse the full Hydraulic Adapters range for the complete family, or contact us to request a quote, mill test reports, and samples.