4N NPT Male Plug – Hex Head NPT Pipe Blanking 4N Adapter

A 4N adapter is an NPT male plug: a hex head plug with an American tapered pipe thread that closes a pipe port by wedging into the thread and sealing on the thread flanks. It is a blanking device with a closed body and no through passage, so nothing flows through it. The seal at this end is made on the thread itself, which is why an NPT plug needs a thread sealant or a dryseal thread rather than the metal cone seat used by the JIC families.

Core Advantages

• Closes an NPT pipe port by the same tapered-thread seal the port was cut for.
• Nine published sizes from Z1/8″X27 to Z2″X11.5, covering the common ANSI/ASME B1.20.1 pipe sizes.
• Closed body with no bore, so the part is a full blanking device and not a restrictor.
• Hex head S1 for standard wrench tightening and removal, with no special tool.
• Carbon steel with trivalent chromium zinc plating, or 304 / 316 stainless steel for corrosive service.
• Turned from bar stock with the taper thread gauged batch by batch before packing.

1. What a 4N Adapter Does

The 4N adapter is a hydraulic plug adapter that closes a pipe port. It is a hex head NPT male plug: one end carries an American tapered pipe thread marked E on the series drawing, and the rest of the part is a solid body with a hex. Where a normal adapter joins two lines, this one ends a single line, so it belongs to the blanking group of the catalogue rather than to the conversion group.

Both sides of the joint still have to match exactly. The pipe size and the thread pitch of the plug have to agree with the port it is turned into, and the port has to be an NPT port. That agreement is the precondition for eliminating leakage at the plugging point. A plug that starts by hand but bottoms out early, or a plug forced into a port of a different thread family, will weep or will damage the port.

The sealing principle of this series is the NPT dryseal taper thread. Both the plug thread and the port thread are tapered, so as the plug is turned in, the thread flanks wedge together and the joint becomes pressure-tight along the engaged threads. The joint is normally completed with a thread sealant, or with an NPTF dryseal thread form made to SAE J476 where a sealant-free joint is required. The 4N adapter does not seal on a 74 degree cone, on a 37 degree flare, on a flat face or on an O-ring, and there is no elastomer in the joint unless the installer adds a sealant.

Where a port has to be closed, the choice between a solid plug such as this one and a hollow hex plug is a question of access and of profile. The 4N is a hex head plug, so it needs wrench clearance around the port; it is the usual choice where the port sits on an open face, where a firm external wrench purchase is wanted, and across the full pipe size range up to Z2″.

2. 4N Specifications

The two ends of this series are described below as a mirrored pair. The first block is the connection that is made to the port. The second block is the closed end, which is not a connection in the ordinary sense but is presented so that a buyer can see exactly what the part does and does not provide.

2.1 Connection 1 – NPT male taper thread, external thread E

• Thread standard and family: ANSI/ASME B1.20.1, general purpose pipe threads, NPT taper thread. The dryseal form of the same joint is covered by SAE J476, where the joint is made pressure-tight on the threads without a sealant.
• Thread sizes available at E: Z1/8″X27, Z1/4″X18, Z3/8″X18, Z1/2″X14, Z3/4″X14, Z1″X11.5, Z1.1/4″X11.5, Z1.1/2″X11.5 and Z2″X11.5. The letter Z in the catalogue notation marks the tapered pipe thread, and the number after X is the pitch in threads per inch.
• Gender: male pipe thread (external), tapered along its length.
• Sealing method: wedging contact between the tapered thread flanks of the plug and the port, completed with a thread sealant, or with a dryseal NPTF thread form where a sealant-free joint is specified. No O-ring, no cone seat and no flat face is used at this joint.
• Mating port standard: an NPT female pipe port of the same nominal pipe size, cut to ANSI/ASME B1.20.1. The port may be in a manifold, a valve body, a cylinder, a pump housing or a pipe fitting.
• Wrench feature: hex S1 is machined on the body, so the plug can be turned in and removed with a standard wrench.

2.2 Connection 2 – Closed blanking end, no port and no through passage

• Connection type: closed. The body ends in a solid turned form behind the hex, so there is no second thread, no second seat and no bore through the part.
• Sizes available: all nine published rows are closed; every 4N part number is a blanking plug and none of them passes flow.
• Gender: not applicable, because no mating part is fitted at this end.
• Sealing method: not applicable at this end. Sealing takes place entirely on the pipe thread described in 2.1.
• Mating part standard: not applicable. What is required on this side of the plug is clearance for the hex head and access for the wrench.

2.3 Construction and Materials

• Body material: this steel hydraulic adapter is offered in carbon steel, 304 stainless steel, 316 stainless steel or brass, selected per order. Brass is a common selection for NPT plugs in water, air and general service lines.
• Plating: trivalent chromium zinc plating (Cr3+) or zinc-nickel plating on carbon steel bodies. Stainless steel bodies are supplied without plating.
• Thread form: the external NPT taper thread is cut or rolled to ANSI/ASME B1.20.1 and inspected with ring gauges so that the thread depth and the taper match the port.
• Seal material: as a steel hydraulic adapter this plug carries no elastomeric seal of its own. Sealing is completed by the tapered thread together with the thread sealant chosen at installation, so any elastomer in this joint comes from that sealant or from a bonded seal used at the port, not from the plug. Where an O-ring is used elsewhere in the same circuit, the published material ranges are approximately -30°C to +100°C for NBR, -20°C to +200°C for FKM and -40°C to +120°C for EPDM.
• Machining process: the plug is turned from bar stock on CNC lathes, the taper thread is produced, the hex is milled or formed, and the part is deburred. Threads are gauged with ring gauges, and the hex, the threaded length and the overall length are checked against the drawing batch by batch before packing.

2.4 Pressure and Temperature

Temperature is governed by the body material and by the thread sealant used, because this hydraulic adapter carries no elastomeric seal of its own. A carbon steel body with zinc plating suits general hydraulic, pneumatic and water service, and 304 or 316 stainless steel is selected for corrosive environments. Where a seal material question arises elsewhere in the same circuit, the published material ranges are approximately -30°C to +100°C for NBR, -20°C to +200°C for FKM and -40°C to +120°C for EPDM elastomers.

Working pressure for a given 4N adapter size is confirmed per order by HENGHUA engineering, based on the thread size, the body wall thickness, the sealing method and the material selected. No single pressure figure is published here for a specific size, because a Z1/8″ plug and a Z2″ plug do not share one rating. An NPT joint is also sensitive to the port it is turned into: a tapered thread wedges, so the strength of the housing around the port, and not only the plug, sets the practical limit for the assembly.

2.5 Part Number and Dimension Table

The table below is the complete published dimension table for the 4N NPT adapter series. Every row is reproduced in printed column order.

What each column means:

• PART NO. is the ordering code. The dash number follows the pipe size step of the series.
• E is the external NPT taper thread of the plug, written in catalogue notation. The Z marks the tapered pipe thread, the fraction is the nominal pipe size, and the number after X is the pitch in threads per inch, so Z1/2″X14 is a 1/2″ NPT thread at 14 threads per inch.
• A is the threaded length of the plug end in millimetres, measured from the end of the plug to the hex as marked A on the series drawing. It shows how much threaded length is available for engagement in the port.
• L is the overall length of the plug in millimetres, from the end of the thread to the outer face of the hex head.
• S1 is the width across flats of the hex head, in millimetres. It is a wrench size, not a thread size, and it grows with the pipe size step.

Thread size and dash chart:

3. How to Read a 4N Part Number

The 4N part number has two parts: the series prefix and the dash size.

• 4N is the series prefix. It identifies the part of this page: an NPT male hex head plug with a closed body, as listed in this table.
• The dash number is the size code, and it follows the pipe size step rather than a tube dash. 02 is the 1/8″ pipe size, 04 is 1/4″, 06 is 3/8″, 08 is 1/2″, 12 is 3/4″, 16 is 1″, 20 is 1.1/4″, 24 is 1.1/2″ and 32 is 2″.
• The dash size fixes the thread and the pitch. 4N-08 carries a Z1/2″X14 thread, which is a 1/2″ NPT thread at 14 threads per inch.
• No suffix is applied to any row in the 4N table. Other series in the same catalogue use suffixes such as -SP, -WD or -PK to mark a variant of that series; if a suffix appears on your drawing, quote the full part number including it.

Worked example using a real row of the table. Part number 4N-08 decodes as follows:

• Series: 4N, NPT male hex head plug.
• Thread E: Z1/2″X14, an American tapered pipe thread of 1/2″ nominal size at 14 threads per inch.
• Threaded length A: 19.5 mm from the end of the plug to the hex.
• Overall length L: 27 mm, and hex S1: 22 mm.
• Function: it closes a single NPT pipe port and passes no flow.

4. Installation and Fitment

The NPT joint of a 4N adapter is made by wedging two tapered threads together. Turn the plug in by hand until it is snug, then tighten with a wrench only as far as the port specification requires. The limit is set by the port rather than by the plug: an NPT thread acts as a wedge, and a plug forced past its seating point loads the housing around the port, which is what splits a cast or thin-walled boss. Stop tightening when the thread is fully engaged.

Thread preparation decides the quality of the joint. Clean the port thread of old tape, old sealant, swarf and oil, and blow it out if the circuit allows. Apply the sealant to the plug thread in the direction of the taper, leaving the first thread or two clean so that no sealant is pushed into the line. PTFE tape or a liquid pipe sealant is the normal choice for NPT; where an NPTF dryseal thread form is used, the joint is designed to seal on the threads without a sealant, but the same clean-thread and alignment discipline still applies. Start the plug by hand, confirm that it turns freely for the first turns, and only then bring a wrench to it.

Reuse is a practical question rather than a rule of thumb. A 4N adapter can be refitted if the thread is clean, undamaged and free of corrosion, and if the port thread is in the same condition. A plug whose thread has been cross-started, stretched by over-tightening or flattened at the crest is not restored by more tape; replace it. Assembly steps:

1. Confirm that the port is an NPT female port of the same nominal pipe size as the plug, and that it is not a BSPT, BSPP or metric port.
2. Inspect the plug thread and the port thread for burrs, flats, corrosion and trapped debris, and check that the port boss is sound.
3. Clean both threads and remove all old tape and sealant, leaving no loose material in the line.
4. Apply the thread sealant to the plug thread, leaving the leading threads clean, and start the plug by hand.
5. Turn the plug in snug, then tighten with the correct wrench on hex S1 only as far as the port specification requires.
6. Leak-check the blanked port at the pressure agreed for the system, and check that the hex head clears adjacent pipework.

Common fitment errors and their symptoms:

• Fitting an NPT plug into a BSPT or BSPP port. The symptom is a thread that starts by hand and then binds, or a joint that weeps no matter how much sealant is used.
• Over-tightening to stop a weep. The symptom is a cracked or distorted port boss, because the tapered thread wedges and the housing takes the load.

5. Applications and Industries

Application tags for this hydraulic plug adapter: hydraulic systems, water jetting, oil and gas, industrial equipment, construction machinery, agriculture, marine and material handling.

Concrete scenarios where a 4N adapter earns its place:

• Blanking spare ports on manifolds, valve blocks and pump housings. Machine tools, hydraulic power units and process skids are commonly built with NPT ports. Each unused port is closed with one plug, so the assembly can be commissioned and the port brought into service later without reworking the housing.
• Capping pipe runs during transport, storage and flushing. A fabricated pipe spool or a pump module that leaves a workshop with open NPT ports can be closed for shipping, keeping dirt, moisture and swarf out of the circuit and protecting the thread from impact.
• Isolating a line for pressure testing. Where one branch of a system has to be closed while another is tested, a plug isolates that branch at the port, using the same thread family as the rest of the pipework.
• General industrial and utility service. NPT ports are common on water, air, coolant and light oil lines in industrial equipment, so a plug in carbon steel or brass is a routine way to close a spare tapping.

The same part suits fluid power circuits, marine deck equipment, construction machinery and material handling systems, provided the mating port is an NPT port of the same nominal pipe size and the fluid suits the body material chosen, supplied as a steel hydraulic adapter in carbon steel, brass or stainless steel.

6. Replacement and Cross-Reference Guide

Replacement selection for this hydraulic plug adapter is organised by thread standard and sealing method, never by brand or catalogue number. An NPT hex head plug is identified by three measurements, and nothing else is needed to find a matching part in the 4N table.

Measure these three things:

1. Measure the port thread: nominal pipe size and pitch in threads per inch. The sizes in this table run Z1/8″X27 to Z2″X11.5, and a matching plug must agree on both the size and the pitch.
2. Check the thread family and the taper. An NPT port takes an NPT plug made to ANSI/ASME B1.20.1. A BSPT port takes a BSPT plug made to ISO 7-1, and a BSPP port takes a parallel BSPP plug made to ISO 228-1. These are not interchangeable even at the same nominal size.
3. Confirm the end configuration. This NPT adapter is a male hex head plug with a closed body. It replaces a worn or damaged NPT hex head plug of the same nominal size. It does not replace a hollow hex plug, a flange plug, a JIC cone plug or a female threaded cap.

Once the three answers are known, choose the row whose E column matches the measured thread. Check A, L and S1 against the port depth and the wrench clearance around it before ordering. Where the port is recessed, or where adjacent pipework leaves no room for a wrench on hex S1, select a hollow hex plug of the same thread instead.

Series that are commonly confused with 4N and are not interchangeable: the SAE J514 JIC 74 degree cone seat family, which seals metal-to-metal on a wide cone face; the SAE J514 JIC 37 degree flare family, which seals metal-to-metal on a conical flare face; the SAE J1926-3 / ISO 11926-3 O-ring boss family, which seals with an O-ring on a straight-thread stud end plus a lock nut; the SAE J1453 ORFS family, which seals on a flat face against an elastomeric O-ring; the ISO 6162 flange plug families, which seal with an O-ring in a flange groove; and the BSPT and BSPP families, which use British thread forms at a different pitch.

7. Ordering, Packaging and Delivery

To order this NPT adapter from the 4N series, give the series code plus the full part number, for example 4N-08, and confirm the following with the enquiry:

• Full part number, including any suffix shown on your drawing or packing list.
• Confirmation that the port is an NPT port of the matching nominal pipe size and pitch.
• Body material: carbon steel, 304 stainless steel, 316 stainless steel or brass.
• Plating for carbon steel bodies: trivalent chromium zinc plating (Cr3+) or zinc-nickel plating.
• Quantity and the required delivery date.

Parts are packed in labelled bags or boxes carrying the full part number, with cartons marked for size and quantity, and the taper thread protected so that it arrives free of burrs, for distributor shelves or for direct-to-line OEM delivery. Sample orders and mixed-size trial orders are accepted before a production release, and custom sizes and drawing-based manufacture can be quoted for OEM programmes. Lead time is confirmed per order.

8. FAQ

What is the difference between JIC 37° flare and ORFS, and which should I use? A JIC 37° flare fitting seals metal-to-metal on a conical flare face and is specified by SAE J514 in the SAE 37° flared family. An ORFS fitting, specified by SAE J1453, seals on a flat face against an elastomeric O-ring held in a groove. Use the family that matches the port on your equipment. Neither one is a substitute for this plug, which closes a tapered NPT pipe port by wedging on the thread.

Can NPT and BSPT be interchanged? No. NPT is an American tapered pipe thread made to ANSI/ASME B1.20.1, and BSPT is a British tapered pipe thread made to ISO 7-1. They differ in thread form and pitch, so the same nominal size will often start by hand and then bind, and the joint will weep. Where a BSPT or BSPP port has to be blanked, use a plug from that family rather than forcing an NPT plug into it.

How do I identify the correct 4N adapter size? Measure the port thread size and pitch and match it to the E column of the table. A Z1/2″X14 port calls for 4N-08, and a Z3/4″X14 port calls for 4N-12. Pipe sizes are nominal, so check the pitch as well as the size, and confirm that the port is an NPT port rather than a British or metric port before ordering.

What seal material should I select for my fluid and temperature? This plug has no elastomeric seal of its own, because the NPT joint seals on the engaged thread flanks together with the sealant used at installation, so the material decision here is the body and the plating. Carbon steel with trivalent chromium zinc plating suits general service, brass is common for water and air, and 304 or 316 stainless steel is selected for corrosive environments. Where an elastomer is used elsewhere in the same circuit, the published ranges are approximately -30°C to +100°C for NBR, -20°C to +200°C for FKM and -40°C to +120°C for EPDM.

How is the working pressure of this adapter determined? Working pressure is confirmed per order by HENGHUA engineering, based on the thread size, the body wall thickness, the sealing method and the material selected. Because a Z1/8″ plug and a Z2″ plug do not share one rating, no single figure is published for the whole series.

What is the minimum order quantity and can I get samples? Sample orders and mixed-size trial orders are accepted for validation before a production release. Minimum order quantity depends on the size, the material and the plating selected, and it is confirmed with the quotation. Send the full part number and the quantity you need, and the order desk will quote the smallest practical release quantity for that configuration.

How much thread sealant should I use on an NPT plug? Apply a thin, even film of PTFE tape or liquid pipe sealant to the plug thread in the direction of the taper and leave the first thread or two clean, so that no sealant is pushed into the line. Excess sealant raises the thread off its flanks, distorts the engagement and can carry loose material into the circuit. Where an NPTF dryseal thread form is specified, the joint is designed to seal on the threads without a sealant, and the thread is then kept clean and dry.

Does an NPT plug let any fluid through? No. The body is closed and there is no bore through the part, so it is a full blanking device and not a restrictor, an orifice or a vent. If a port has to be closed while leaving a small controlled passage, that is a different part type and should be specified by drawing or as a special.

Send the full 4N adapter part number, the port size and the quantity you need, and HENGHUA will confirm the drawing, the material and the lead time with the quotation.

Related series in the same family: the 4NN adapter (plug) and the 1N adapter (straight). Browse the full Hydraulic Adapters range for the complete SAE J514 JIC, NPT, ORFS and ISO 6162 flange families.