7N Adapter – NPT Female to NPT Female Hydraulic Adapter with a Tapped Thread at Both Ends

The 7N adapter is a straight hydraulic adapter with an internal NPT taper thread tapped into each end, so it presents a female pipe thread on both sides. There is no male thread, no cone and no O-ring on the part: the 7N adapter is a tapped sleeve that joins two male NPT pipe threads, and the two ends are marked E and F on the drawing. Typical duties are extending a port outward into clear space, changing from one pipe size to another between two male ends, and making a port change without introducing a swivel.

Both tapped ends must match the mating male threads exactly in thread form, nominal size and pitch, because that match is the precondition for eliminating leakage at the conversion point. A part with a taper thread of the wrong family will start on the mating thread and still weep under pressure.

Sealing principle of this series: pressure tightness is made on the thread flanks as each male taper is drawn into the tapped taper. The joint needs a sealant applied to the male thread, or an NPTF dryseal thread pair per SAE J476. This series does not seal on a 37° flare, on a 74° cone, on an O-ring face, on an elastomeric seat or on a four-bolt flange.

Core Advantages

• Internal NPT thread at both ends, so the part is used where both mating connections are male pipe threads.
• Tapped sleeve body with no male thread and no elastomer, so there is no cone, face or seal to crush in service.
• Port extender function: it moves a connection outward so a hose tail can be started and a wrench can reach.
• Swivel-free port change: the adapter turns onto the first male thread, then the second male part screws in without rotating.
• 17 printed sizes, Z1/8″X27 through Z2″X11.5, in equal and unequal combinations.
• Carbon steel with trivalent chromium zinc plating, or 304 / 316 stainless steel for corrosive service.

1. What a 7N Adapter Does

An NPT adapter in this series joins two male NPT pipe ends on a single axis. What enters the E end leaves the F end on the same centre line, so the part changes the size or the position of a connection but never its direction.

The female end is a tapped thread. That means the thread is cut inside the body: the male pipe thread of the mating part is screwed into it, and the seal is formed on the flanks of that male thread as it is drawn into the taper. Nothing on the outside of the 7N adapter seals, which is why a sealant is applied to the mating male thread and not to the adapter. This is the single most important thing to understand about a female-only part: the adapter supplies the thread, the mating male part supplies the seal.

The first duty of the series is as a port extender. When a port is recessed, surrounded by other fittings or too close to a wall, the male hose tail cannot be started squarely and the wrench has no room to swing. The tapped sleeve is screwed onto the existing male thread and presents a fresh female thread further out, in clear space, so the hose tail is made up where it can be aligned and tightened properly.

The second duty is a port change with no swivel. With a female end at each side, the adapter is turned onto the first male thread, and the second male part is then screwed into the free end. The second part never has to rotate, so a hose assembly or a rigid tube can be connected without a swivel joint and without twisting the line. This is therefore the alternative when a swivel nut adapter is not wanted in the circuit.

The third duty is a size change between two male pipe ends, where the part acts as a coupling. Rows such as 7N-08-12 take a Z1/2″X14 male thread at one end and a Z3/4″X14 male thread at the other.

Because there is no seat angle and no elastomer in this series, there is nothing to deform but the threads themselves. Thread condition therefore governs the result: a flattened or corroded thread leaks no matter how much sealant is applied.

2. 7N Specifications

The two ends are presented as mirrored blocks. Read the E block for the first pipe end and the F block for the second, then confirm both against the mating male threads of this NPT adapter.

2.1 Connection 1 – NPT female taper thread, E end

• Thread standard and family: American tapered pipe thread NPT to ANSI/ASME B1.20.1, with NPTF dryseal threads to SAE J476 as the pressure-tight option.
• Thread size range available at E: Z1/8″X27 through Z2″X11.5, in the steps printed in table 2.5.
• Gender: female, an internal tapped thread.
• Sealing method: metal-to-metal contact on the thread flanks of the mating male thread, with a sealant applied by the installer.
• Mating connection standard: a male NPT or NPTF pipe thread of the same nominal size and pitch, such as a hose tail, nipple or male stud.

2.2 Connection 2 – NPT female taper thread, F end

• Thread standard and family: American tapered pipe thread NPT to ANSI/ASME B1.20.1, with NPTF to SAE J476 as the dryseal option.
• Thread size range available at F: the same nine steps as connection 1, from Z1/8″X27 to Z2″X11.5.
• Gender: female, an internal tapped thread.
• Sealing method: metal-to-metal contact on the thread flanks of the mating male thread, with a sealant applied by the installer.
• Mating connection standard: a male NPT or NPTF pipe thread of the same nominal size and pitch.

Both ends of this female adapter are identical in form; only the size differs in the unequal rows. There is no male end and no seat anywhere on the part, so the E and F columns describe two tapped ports rather than two studs.

2.3 Construction and Materials

The body is machined from bar stock on CNC lathes as a sleeve, then drilled through and tapped with the NPT taper at each end. The hex is formed so the body can be held while both male threads are made up.

• Body material: carbon steel as standard; 304 stainless steel, 316 stainless steel or brass on request.
• Plating: trivalent chromium zinc plating (Cr3+) for carbon steel as standard; zinc-nickel plating available. Plating thickness and corrosion performance are confirmed per order rather than published as a series figure.
• Seal material: this adapter fitting carries no elastomer, no O-ring and no bonded washer. Pressure tightness comes from the thread pair plus the sealant chosen by the installer, so seal material selection applies to the sealant rather than to the body.
• Machining process: bar-stock turning, through-drilling, NPT taper tapped at both ends and gauged, then deburred.
• Hex feature: a single hex (S1) across the body, from 17 mm to 70 mm across flats depending on size. There is no bulkhead feature and no swivel in this series.

2.4 Pressure and Temperature

Working pressure for this series is not set by the series code. It is governed by the thread size, the wall thickness of the sleeve, the sealing method and the material selected, and it is limited by the two mating male threads. Working pressure for these sizes is confirmed per order by HENGHUA engineering, based on the thread size, sealing method and material selected.

Temperature is a question of the body material and the sealant rather than of an elastomer, because the part contains none. Published material ranges of the elastomers used elsewhere in the same circuit are approximately -30°C to +100°C for NBR, -20°C to +200°C for FKM (Viton-type) and -40°C to +120°C for EPDM. Carbon steel with zinc plating suits general hydraulic service; specify 304 or 316 stainless steel for corrosive or offshore environments.

2.5 Part Number and Dimension Table

The table below is the complete printed size range of the 7N series. All dimensions are in millimetres. Both the E and the F column describe an internal tapped thread.

What each column means

• PART NO. – the HENGHUA part number. The prefix 7N is followed by one size code, or by two size codes separated by a dash when the two tapped ends differ in size.
• E – the tapped thread of connection 1. Z marks the American tapered pipe thread, the fraction is the nominal pipe size and the number after X is the pitch in threads per inch, so Z3/8"X18 is a 3/8″ NPT internal thread at 18 threads per inch.
• F – the tapped thread of connection 2, in the same notation. When E and F are identical the part is equal ended; when they differ the part steps between two pipe sizes.
• L – the overall length of the adapter in millimetres, from the outer face of the E end to the outer face of the F end. It is the distance the connection is extended.
• S1 – the hex across flats in millimetres, the wrench size used to hold the body while both male threads are made up.

Thread size and dash chart

The dash code is the size step. The equal-ended rows of this series are:

No note lines are printed under this table.

3. How to Read a 7N Part Number

A 7N part number has two elements: the series prefix and one or two size codes, with no suffix on this series.

The prefix 7N identifies the family: a straight female adapter with a tapped NPT thread at both ends. A different prefix in the same catalogue identifies a different geometry, such as the male-ended version of the same thread family, an elbow body or a plug.

The first size code is the E end and the second, when present, is the F end. Both are pipe dash numbers: 02 means 1/8″, 04 means 1/4″, 06 means 3/8″, 08 means 1/2″, 12 means 3/4″, 16 means 1″, 20 means 1.1/4″, 24 means 1.1/2″ and 32 means 2″. A single code means a swept sleeve with the same tapped thread at both ends.

Worked example: 7N-08-12.

• 7N – straight female-to-female NPT adapter with a tapped thread at each end.
• 08 – connection 1 is the tapped Z1/2″X14 thread.
• 12 – connection 2 is the tapped Z3/4″X14 thread.
• From the table: L is 43 mm and the hex S1 is 36 mm.

A buyer ordering 7N-08-12 therefore receives a tapped sleeve that couples a 1/2″ male pipe thread to a 3/4″ male pipe thread, with a 36 mm hex for holding the body. No suffix is applied to any row of this table; if a suffix appears on your drawing, quote the full part number including it.

4. Installation and Fitment

An NPT joint is made by drawing a tapered male thread into a tapered female thread until the flanks lock, so tightening is a feel-and-angle operation rather than a flat torque figure. HENGHUA does not publish a single torque figure for the series. Follow the port maker’s recommendation, or confirm the figure with HENGHUA per order.

Sealant, not tape fragments. Thread preparation matters more on this series than on a flared or O-ring family, because the thread is the seal at both ends. Clean both male threads, dry them, and apply a sealant compatible with the fluid and the system temperature. Leave the first thread at each entry clean so no tape fragment can enter the circuit.

Alignment. Bring the first male thread in finger-tight and check that the run of the line is straight before snugging the hex S1. Then bring the second male thread in finger-tight. Forcing a misaligned male thread binds the taper and produces a weep along the thread.

Contamination and reuse. Cap both tapped ends before storage, because debris that reaches the thread flanks scores them. The body can be reused if both tapped threads are undamaged, but the joint is made up again with fresh sealant because the old sealant no longer fills the flanks.

Common fitment errors and their symptoms:

• Forcing an NPT male thread into a BSPT tapped end. Symptom: the threads bind after two or three turns and then weep.
• Using a 7N adapter where a flared or O-ring part is required. Symptom: no seal at all, because no seat and no elastomer exist at either end.
• Over-tightening to stop a weep. Symptom: a cracked port boss or a split tapped thread, because a forced taper generates high hoop stress.
• Reusing the joint without renewing the sealant. Symptom: a slow weep that grows with thermal cycling.

Six-step assembly

1. Confirm that both mating parts are male NPT or NPTF threads of the same nominal size and pitch as the E and F ends.
2. Inspect both tapped threads for nicks and debris, and check the taper with a thread gauge where available.
3. Clean both tapped threads and the mating male threads, and remove old sealant.
4. Apply the selected sealant to the first male thread, starting one thread back from the end.
5. Fit the adapter hand-tight, hold the hex S1 with the correct wrench, and snug the joint without forcing it.
6. Apply sealant to the second male thread and make up the second joint, then leak-check both ends at the system pressure and re-check after the first thermal cycle.

5. Applications and Industries

Application tags for this series: hydraulic systems, water jetting, oil and gas, industrial equipment, construction machinery, agriculture, marine, material handling. An NPT adapter of this type is specified by its two pipe threads rather than by industry, so one part serves several sectors.

Port extension in crowded manifolds. When a manifold port is surrounded by other fittings, this tapped sleeve moves the connection outward and gives the installer room to start a hose tail squarely and swing a wrench. That is the most common reason for a female-only part in a hydraulic system.

Swivel-free assembly. Where a rigid tube or a pre-made hose assembly cannot be rotated, a 7N adapter is turned onto the fixed male thread first, and the assembly is then screwed into the free end without rotating. The line stays aligned and the circuit needs no swivel joint.

Pipe size change between two male ends. A pump with a 1/2″ male outlet and a hose assembly with a 3/4″ male tail meet through one 7N-08-12, which replaces a stack of a coupling and a bushing.

Repair and replacement. Maintenance crews keep equal-ended rows on the shelf as general coupling stock, because a damaged male thread on a line can often be recovered by coupling through a tapped sleeve rather than replacing the whole line.

6. Replacement and Cross-Reference Guide

Cross-reference for this series is organised by standard and sealing method, never by brand. Two pipe-threaded parts interchange only if the thread form, the nominal size, the pitch and the gender all match.

A 7N adapter is a female-to-female NPT part under ANSI/ASME B1.20.1, with a tapped thread at each end. It is not the same part as a male-ended thread adapter of the same family, and it is not interchangeable with the male-to-female version, which has one stud end and one tapped end. It is not interchangeable with a JIC part, which seals on a 37° or 74° seat under SAE J514, nor with an ORFS part, which seals a flat face against an elastomeric O-ring under SAE J1453, nor with a BSPT part, which is a 55° taper thread under ISO 7-1.

To identify the correct replacement, measure three things.

1. Thread. Measure the outside diameter and pitch of the mating male thread, and confirm that both ends of the replacement are the same nominal size and pitch.
2. Gender. Confirm that both mating parts are male. A female adapter cannot be fitted to a female port, and a thread adapter with one male end belongs to a different series.
3. Thread form. Confirm that the port is a 60° NPT taper and not a 55° BSPT taper or a straight thread. A straight thread with an O-ring groove belongs to the SAE J1926 or ISO 6149 family and needs a different part.

Where the mating port standard is not NPT, a cross standard adapter of the same size is the correct part rather than a forced thread. Record the measurements with the part number so HENGHUA can match a printed size code.

7. Ordering, Packaging and Delivery

To order, give the following information:

• Series code: 7N.
• Full part number, for example 7N-08-12, taken from table 2.5.
• The two tapped thread sizes, read from the E and F columns.
• Sealant or dryseal thread requirement, if the joint is specified as NPTF.
• Body material and plating: carbon steel with trivalent chromium zinc plating, zinc-nickel plating, or 304 or 316 stainless steel.
• Quantity, destination and the packing format required.

Packaging formats: bulk cartons for line-side consumption, small boxes for distributor shelves and labelled bags for service kits, each labelled with the part number, the thread sizes and the quantity. Sample orders and first-article parts are available for OEM programmes, including drawing-based manufacture of specials.

Lead time is confirmed per order and depends on size, material, plating and quantity. As a hydraulic adapter manufacturer and hydraulic adapter supplier, HENGHUA can quote this female adapter, the matching sealant recommendation and the packing format as one supply.

8. FAQ

Why is a 7N adapter female at both ends?

A female-only design is used where both mating parts are male pipe threads, and where the line has to be connected without rotating either side. Because the adapter is turned onto the first male thread and the second male part then screws into the free tapped end, the part changes the size or the position of a port without adding a swivel joint. Both ends are tapped threads, so this thread adapter seals on the flanks of the mating male threads.

What is the difference between JIC 37° flare and ORFS, and which should I use?

A JIC 37° flare joint seals metal-to-metal on a 37° conical flare face under SAE J514. An ORFS joint seals a flat face against an elastomeric O-ring under SAE J1453. Choose the family that matches the port already on the equipment, because the two are not interchangeable. This series is in neither family: it is a taper pipe thread that seals on the thread flanks.

Can NPT and BSPT be interchanged?

No. NPT is a 60° taper pipe thread under ANSI/ASME B1.20.1, and BSPT is a 55° taper pipe thread under ISO 7-1. The form, angle and pitch differ, so the two will not seal even when a few threads start by hand. Use the thread the port is machined to, and order a cross standard adapter when the two sides differ.

How do I identify the correct 7N size?

Measure the outside diameter and pitch of both mating male threads, then read across the E and F columns of table 2.5. When both threads match a printed row, that row is the correct part number. Confirm the thread form as well, because a straight thread with an O-ring groove looks similar at a glance but belongs to a different family.

What seal material should I select for my fluid and temperature?

This part contains no elastomer, so the material decision is the sealant rather than an O-ring. Select a sealant compatible with the fluid and the system temperature, and apply it to the mating male threads. If the same circuit uses elastomer-sealed components, the published ranges are approximately -30°C to +100°C for NBR, -20°C to +200°C for FKM (Viton-type) and -40°C to +120°C for EPDM.

How is the working pressure of this adapter determined?

Working pressure is not fixed by the series code. It is governed by the thread size, the wall thickness of the sleeve, the sealing method and the material selected, and it is limited by the two mating male threads. Working pressure for these sizes is confirmed per order by HENGHUA engineering, based on the thread size, sealing method and material selected.

Can a 7N adapter be used to extend a recessed port?

Yes, and that is one of its main duties. The tapped sleeve is screwed onto the existing male thread and presents a fresh tapped thread further out, in clear space, so the hose tail can be started squarely and tightened with a full wrench swing. Choose the size from table 2.5 so that the extension leaves enough room for the second joint and for the wrench.

What is the minimum order quantity and can I get samples?

Minimum order quantity depends on the size code, the material and the plating, so it is confirmed with the quotation rather than published as one series figure. Samples and validation parts are available for OEM and distributor evaluation, including specials made to a drawing.

Send your requirement to HENGHUA

Send the part number, both tapped thread sizes, the sealant or dryseal requirement, the material and plating, and the quantity. HENGHUA confirms the match to the printed table, the seal options and the delivery schedule, and quotes the 7N adapter that fits your circuit.

Related series in the same family: the 5N adapter (straight) and the 1N adapter (straight). Browse the full Hydraulic Adapters range for the complete SAE J514 JIC, NPT, ORFS and ISO 6162 flange families.