Straight Bulkhead Fitting Adapter 6C / 6D (Panel and Tank Wall Mounting, 6C-LN / 6C-RN)

Why This Straight Bulkhead Fitting Adapter 6C / 6D Is the Cleanest Way Through a Wall

The straight bulkhead fitting adapter 6C / 6D is a straight fitting designed to pass through a panel, a frame member or the wall of a reservoir, and to be locked on both sides of that wall with nuts. One end connects to the hydraulic line outside the wall, the other end connects inside it, and the wall itself is sealed where the fitting body passes through. Nothing is welded, nothing is brazed, and nothing has to be cut into the panel to make the joint.

That is why the part exists. Running a line through a steel panel with a welded boss means a welding operation inside a machine, heat input near seals, and a repair that cannot be undone. The straight bulkhead fitting adapter 6C / 6D replaces all of it with a hole, a fitting and two nuts, which can be assembled, tightened, inspected and removed with ordinary hand tools.

The family is offered in two series and two nut variants. 6C is the light L series and 6D is the heavy S series, matched to the tube and port standards in use. The 6C-LN and 6C-RN variants differ in the nut hardware supplied with the fitting, and both are described in the variant section below.

Core Advantages

1. No welding, no brazing — the fitting is mechanically locked through the wall with nuts, so installation carries no heat input and no permanent change to the panel.
2. Serviceable from both sides — the fitting can be loosened, re-sealed and re-torqued without cutting the line or opening the reservoir.
3. Sealed at the wall, not at the thread — the wall joint uses a designed sealing face and washer, so leak paths do not depend on thread sealant or tape.
4. Two nut variants cover both installation realities — 6C-LN for standard wrench access and 6C-RN where a low-profile retaining nut is required.
5. Light L and heavy S series in one family — 6C and 6D cover both tube standards, so a mixed-standard machine needs one spare line per size.
6. Traceable, and cross-referenced free of charge — send the panel drawing, the old part number or a photograph and we will confirm the series, the variant and the lead time within 24 hours.

Technical Specifications

What Is a Bulkhead Fitting?

A bulkhead fitting is a straight adapter with a threaded mounting section in the middle of its body. The fitting passes through a drilled hole, a washer or seal is placed against the wall face, and a nut is threaded onto the mounting section on the far side. Tightening the nut pulls the fitting shoulder against one face of the wall and compresses the seal against it, so the fitting is mechanically anchored and the wall joint is sealed at the same time.

Both ends of the straight bulkhead fitting adapter 6C / 6D are working connections: one faces the line outside the wall and one faces the line inside. The fitting therefore carries a pressure boundary through the wall in a single machined component, with no intermediate joints, no welded boss and no adapter stack.

Connection 1 — Line Connection

Connection 2 — Inside Connection

Mounting Section — Wall Joint

6C-LN and 6C-RN Variants

Two nut variants are catalogued for this fitting family, and the suffix is part of the order code:

Both variants use the same body and the same mounting thread. What changes is the nut that arrives with the fitting and, in some sizes, the washer or sealing hardware that goes with it. Three practical consequences follow:

1. Order the suffix, do not leave it to chance. A 6C-LN and a 6C-RN of the same size are not interchangeable from a packaging point of view, even though the body is the same. State the suffix on the enquiry so the correct nut ships and the correct part number is marked on the fitting.
2. Check the cavity before choosing the variant. Measure the distance from the inside face of the panel to the first obstruction. If it is tighter than the hex nut height plus wrench clearance, specify 6C-RN.
3. Confirm the thread and the panel hole together. The panel hole, the mounting thread, the nut and the sealing washer form one joint; a change in any of the four must be checked against the others.

The nut hardware described above is the standard practice for the LN and RN variants of this family. Confirm the exact nut, washer and mounting thread against the specification table and your panel drawing before release. [to be confirmed]

Dimensional Data

Full Part Number Matrix

The table above is transcribed in full from the 6C / 6D specification drawing: 10 light series L rows and 10 heavy series S rows, each carrying both metric threads E and F, the tube outside diameters D1 and D2, the dimensions l1, l2, L1 and L2, the hexes S1, S2 and S3 plus S4, and the pressure grade printed against that row. On this drawing the LN and RN variants share the same body matrix, so the variant letter is added to the PART NO. at order and does not change the row data.

Materials and Finish

Working Pressure and Operating Envelope

The working pressure of a straight bulkhead fitting adapter 6C / 6D is governed by the smallest wall section in the component — normally the mounting thread where it passes through the wall — and by the tube, port and mating connectors on either side. A bulkhead joint also carries a mechanical load that a port joint does not: the nuts clamp the fitting into the panel, and the panel must be stiff enough to hold that clamp load without deformation.

Panel thickness matters for a second reason. The mounting thread must be long enough to accept the nut with the seal compressed, and a thin panel with a long mounting thread needs the correct washer stack. State the panel material and thickness on the enquiry and we will confirm the mounting thread length, the nut and the sealing hardware for that combination. Request the size-specific pressure table at the same time and we will return the rating for the exact thread, series and panel preparation.

Installation Notes for the Straight Bulkhead Fitting Adapter 6C / 6D

1. Drill the hole to the mounting thread size and deburr both faces. A raised burr prevents the seal from seating against the panel.
2. Fit the sealing washer or O-ring against the panel face on the shoulder side of the fitting.
3. Insert the fitting through the hole and hold it square. Angling the fitting deforms the seal before the nut is even started.
4. Fit the mounting nut — hex lock nut on the 6C-LN variant, retaining nut on the 6C-RN variant — and tighten to the specified torque while holding the body flats.
5. Make up both line connections to their own torque values, using two wrenches so that the panel joint is not disturbed.
6. Pressure-test the wall joint specifically. A bulkhead leak usually appears at the panel face rather than at either line connection, so watch the wall and not only the fittings.
7. Re-check the mounting nut after the first thermal cycle on machines that run hot, since the panel and the fitting expand at different rates.

Applications

The straight bulkhead fitting adapter 6C / 6D is specified wherever a hydraulic line has to cross a structure:

• Reservoir tanks and hydraulic power units, where the line passes through the tank wall
• Machine frames and guards, where tube runs pass from enclosure to enclosure
• Mobile equipment chassis members and bulkheads with limited access behind the panel
• Test stands and skids built from modular frames, where line routing changes with each project
• Repair work, where a welded boss has failed and a mechanical replacement is needed without hot work

In each case the objective is a line through the wall that is sealed, serviceable and reversible.

Quality, Testing and Traceability

Every straight bulkhead fitting adapter 6C / 6D is machined from controlled steel stock, and thread form, shoulder squareness, mounting thread length and nut concentricity are checked as part of the normal production flow. Assemblies are pressure tested, batch labels allow a supplied fitting to be traced back to the material lot, and material test reports, dimensional inspection records and third-party inspection arrangements are available on request. OEM laser marking of part numbers or customer references can be applied where the quantity supports it.

Ordering Information

To order, specify six things:

1. Série — light L (6C) or heavy S (6D)
2. Variant — 6C-LN (hex lock nut) or 6C-RN (retaining nut)
3. Line connection thread — the thread at Connection 1
4. Inside connection thread — the thread at Connection 2
5. Panel details — panel material and thickness, so that the mounting thread length can be confirmed
6. Quantity and marking — including any customer reference that has to be laser marked

Standard catalogue sizes ship from stock in either variant; non-standard thread pairs and extended mounting threads are machined to order.

FAQ

What is the difference between 6C-LN and 6C-RN? They are the same fitting body with different nut hardware. 6C-LN ships with a hex lock nut for the mounting thread and suits normal wrench access. 6C-RN ships with a retaining nut of reduced profile for shallow or crowded cavities behind the panel. 

Can I use the fitting without a sealing washer at the panel? No. The wall joint has to be sealed at the panel face; thread sealant applied to the mounting thread is not a substitute for the designed seal.

Do I have to weld anything to install the straight bulkhead fitting adapter 6C / 6D? No. Drilling the mounting hole is the only panel preparation. This is the main reason the mechanical bulkhead fitting is chosen over a welded boss on machines that are already assembled.

What panel thickness suits the standard mounting thread? It depends on the size. Send the panel thickness and material and we will confirm the mounting thread length, the nut and the washer stack for the joint.

Can the fitting be re-used if the panel is later replaced? Yes. The fitting body and the nut are reusable as long as the mounting thread and the shoulder are undamaged and a new wall seal is fitted.

Request a Quote for the Straight Bulkhead Fitting Adapter 6C / 6D

Send us the panel drawing, the old part number or a photograph of the fitting being replaced, and we will confirm the series, the variant (6C-LN or 6C-RN), the threads and the lead time within 24 hours. Please include the panel material and thickness, the working pressure and the operating temperature so that we quote the correct mounting thread and material rather than a nominal equivalent. Mating connectors, mounting nuts and wall seals are available on the same order.

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