1H Metric Male L-Series ISO 6149-3 Straight Adapter – 1H Adapter

The 1H adapter is a straight hydraulic adapter with a metric male ISO 6149-3 O-ring stud end at each end, so it joins two ports of the same thread size using an elastomer O-ring as the seal at both ends. It belongs to the metric L series, the light duty metric stud end family, and it is the direct metric counterpart of the BSP and SAE straight-thread O-ring families. This page gives the printed dimension table, the sealing principle, the L series against S series comparison, the printed port note and the installation rules for the 1H adapter.

Core Advantages

• Two identical ISO 6149-3 L series stud ends on one straight body, so the same fitting joins two ports of the same size.
• Metric O-ring sealing per ISO 6149, where the thread clamps and the O-ring in the port recess does the sealing.
• Ten sizes from M10X1 to M48X2 with a single hex between the two stud ends.
• Matches an ISO 9974-1 port as supplied, or an ISO 6149-1 port when the retaining ring is not used.
• Carbon steel with trivalent chromium zinc plating, or 304 / 316 stainless steel for corrosive duty.
• Seal material options of NBR, FKM and EPDM to match the fluid and temperature window.

1. What a 1H Fitting Does

A 1H adapter is a straight male-to-male adapter: a single machined body with a metric threaded stud end at each end and a hex in the middle, used to join two ports that both accept the same metric O-ring stud end. Each end carries its own O-ring groove, and each end seals in the machined recess of its own port. Because both stud ends are the same size by design, the part is a coupling with no size change between the two sides.

The core value of this part is dimensional match. Each sealing end has to match its mating port exactly, because that match is the precondition for eliminating leakage at the joint. A stud end made to ISO 6149-3 has a defined thread length, a defined groove position and a defined shoulder, and a port made to ISO 6149-1 or ISO 9974-1 has a matching recess; when the two are matched, the O-ring is compressed by a controlled amount and the shoulder stops against the port face.

The sealing principle of this series is a straight metric thread with an elastomeric seal. In the ISO 6149 family the thread is a clamp only: it holds the stud end in position and resists pressure load, while the O-ring compressed in the port recess does the sealing work. The thread itself is not a sealing element, which is why thread tape or paste is not used on this joint and why the connection can be dismantled and rebuilt without changing its sealing behaviour.

2. 1H Specifications

2.1 Connection 1 – Metric Male ISO 6149-3 L Series Stud End

Connection 1 is a metric male stud end with a parallel metric thread to ISO 6149-3, the light duty metric stud end standard. The printed range covers M10X1, M12X1.5, M14X1.5, M16X1.5, M18X1.5, M22X1.5, M27X2, M33X2, M42X2 and M48X2, ten sizes from the smallest metric port in the range up to M48. The thread is male and external, and the stud end carries an O-ring groove behind the lead thread.

Sealing is by an elastomer O-ring on the stud end, compressed in the machined recess of the mating port face. The mating port is a metric port with an O-ring recess as described by ISO 6149-1, and the printed note on the chart records that the stud end also fits an ISO 9974-1 port, or an ISO 6149-1 port when the retaining ring is not used. The O-ring column of the table lists the ring for this end as O-RING E.

2.2 Connection 2 – Metric Male ISO 6149-3 L Series Stud End

Connection 2 is the mirror image of connection 1. It is the same metric male ISO 6149-3 stud end, with the same thread size as connection 1 on every row of the printed range, the same O-ring groove and the same sealing principle in its own port recess. The table lists it separately as thread F and O-RING F, and for every part number in the range E equals F and the E ring equals the F ring.

Presenting the two ends separately matters because it makes the part easy to specify against a drawing. A buyer can confirm from the table that A and B are equal for each size, that the two rings are the same, and that the part introduces no size change. If a future requirement calls for two different thread sizes on one body, that is a different series rather than a variant of this one.

2.3 Construction and Materials

The body is machined from bar stock on CNC lathes, so both threads, both O-ring grooves and the hex are produced to a common centreline and stay concentric. The hex is dimension S1 in the table and runs from 14 mm on 1H-10 to 55 mm on 1H-48. It sits between the two stud ends, so it is gripped from the side while the part is run into a port.

There is no third connection, no branch and no through-drive feature; the internal bore of the adapter is a straight passage that connects the two ports. The O-ring groove on each stud end is a machined feature rather than a loose accessory, so the ring cannot be lost during transport and cannot be left out by mistake at the point of assembly.

Body material options are carbon steel, 304 stainless steel, 316 stainless steel and brass. The standard export build is carbon steel with trivalent chromium zinc plating (Cr3+), with zinc-nickel plating available where a harder finish is preferred. Stainless steel is selected for corrosive environments, offshore and marine work and water-based fluids. Plating thickness and salt-spray performance are not stated here and are confirmed per order. Seal options are NBR, FKM and EPDM, and replacement O-rings can be supplied separately. Every batch is checked against the drawing with thread gauges and dimensional checks before packing.

2.4 Pressure and Temperature

Working pressure for these sizes is confirmed per order by HENGHUA engineering, based on the thread size, sealing method and material selected. The printed chart carries no pressure column, so no per-size rating is quoted on this page. On a straight-thread O-ring joint the pressure capability is governed by the port wall and the housing as much as by the adapter, and the L series and S series differ in their stud end proportions rather than in a published pressure figure.

Temperature is a material fact. NBR suits approximately -30°C to +100°C, FKM approximately -20°C to +200°C, and EPDM approximately -40°C to +120°C. The steel body is not the limiting element in normal service; the elastomer is. Select the compound against the fluid first, then confirm the temperature window against the same compound.

2.5 Part Number and Dimension Table

Dimensions are millimetres unless the column states a thread size. Printed note under the table: “Fit for ISO 9974-1 port or ISO 6149-1 port when useless of retaining ring.”

What each column means

• PART NO. – the ordering code, built from the series prefix 1H plus a two digit size code that follows the nominal metric thread size.
• E – the thread size and pitch of connection 1, written as the nominal metric diameter followed by the pitch, for example M14X1.5.
• F – the thread size and pitch of connection 2. In this series F always equals E, because both ends are the same stud end.
• O-RING E – the O-ring for connection 1, printed as O plus inside diameter in millimetres and cord diameter in millimetres, so O11.3X2.4 is a 11.3 mm inside diameter ring with a 2.4 mm cord.
• O-RING F – the O-ring for connection 2, identical to the E ring for every size in the range.
• A – the thread length of connection 1, measured from the sealing face to the end of full thread.
• B – the thread length of connection 2, identical to A for every size in the range.
• L – the overall length from one sealing face to the other.
• S1 – the width across the flats of the central hex, which decides the spanner size.

There is no pressure column and no seat angle column in the printed chart.

Thread size and dash chart

3. How to Read a 1H Adapter Part Number

A 1H adapter part number has two fields: the series prefix and the size code. The prefix 1H identifies the family, a metric male ISO 6149-3 L series O-ring adapter with a stud end at each end of a straight body. The second field is a two digit code that follows the nominal metric thread size.

Worked example, 1H-14: 1H is the series prefix and 14 is the size code, shown in the table as M14X1.5 with thread length A of 11.0 mm, thread length B of 11.0 mm, overall length L of 33 mm, hex S1 of 19 mm, and an O11.3X2.4 O-ring at each end. There is no suffix on this number, because both ends are defined by the series itself. The letter suffix H used elsewhere in the metric programme marks the heavy duty S series form, so a request written as 1H-14H is an ISO 6149-2 S series stud end and not a 1H adapter, and the two forms should not be mixed on one order line.

4. Installation and Fitment

This O-ring adapter is a straight-thread part, so the O-rings are the seals and the threads are only clamps. Do not wrap the threads with PTFE tape, do not brush on a thread sealant or paste, and never fit the part with one O-ring omitted. A sealant adds nothing to a straight-thread joint and can push into the recess and change how the O-ring is compressed, and contamination in that same recess is one of the most frequent causes of a weep on an otherwise correct assembly.

Torque practice is a sequence rather than a number. Confirm both ports are clean, fit the O-rings to their grooves without stretching them, start each thread by hand to prove it is not cross-threaded, then bring the metric adapter in with a spanner until the shoulder contacts the port face. Because the part has two ends, work one end at a time: seat the first, hold the body by the hex, then seat the second. An over-tightened hydraulic adapter distorts the O-ring and can flare the port; an under-tightened one leaves the ring short of its designed compression.

Common fitment errors and their symptoms:

• One O-ring missing. A leak at one end only, present as soon as pressure is applied.
• Ring of the wrong size or cord. An immediate low-pressure leak, or a pinched or cut ring on removal.
• Over-compressed ring. A slow weep that grows with temperature, with a flattened ring inside.
• Debris in the recess. An intermittent weep that changes with pressure cycling.
• Cross-threading. High turning effort before the shoulder lands, with metal particles at the thread.
• Mismatched duty or pitch. The stud end runs in part way and stops, or seats with a visible gap.

Assembly steps:

1. Confirm both ports carry metric threads with an O-ring recess and that the threads match the part.
2. Inspect both recesses for burrs, chips and old seal material, and blow them clean.
3. Check both O-rings for size and cord, and fit them to their grooves without twisting.
4. Lubricate the threads and rings with a light film of system fluid compatible with the compound.
5. Run the first end in by hand, seat that shoulder, then hold the hex and seat the second end the same way.
6. Pressure test, inspect both shoulders and record the seating positions for later refits.

The steel body can be cleaned, inspected and refitted when both threads and both shoulders are undamaged, but the O-rings are single-use elastomer items and should be replaced whenever the part is removed.

5. Applications and Industries

As an ISO 6149 adapter this part suits hydraulic systems, water jetting equipment, oil and gas skids, industrial machinery, construction machinery, agricultural equipment, marine installations and material handling units wherever a metric O-ring port has to be extended or joined to another port of the same size.

Concrete scenarios:

• Manifold to valve connection. A metric O-ring port on a manifold is joined to the matching port on a valve with one straight part, so the assembly stays rigid and compact with no hose in between.
• Extending a port out of a housing. Where a port sits inside a recess and a hose end needs clearance, this straight thread adapter brings the connection out to a defined, accessible position.
• Panel and control block runs. In small control blocks and test rigs, this metric adapter passes a metric O-ring connection through a wall without adding a second seal style to the circuit.

6. Replacement and Cross-Reference Guide

A metric adapter replacement is identified by standard, thread and sealing method, never by brand. The 1H adapter is a metric ISO 6149-3 L series O-ring stud end supplied as a straight thread adapter, so for an O-ring adapter a correct substitute has to match the metric thread and pitch, the ISO 6149 O-ring sealing method, and the stud end dimensions of thread length and shoulder position. Two families can look alike in a photograph and still not interchange, because ISO 9974 and ISO 6149 both use metric threads with an elastomer seal, and the ISO 6149 L series and S series share a port but not a stud end.

L series against S series. The ISO 6149-1 port is common to both, so an L series and an S series stud end of the same thread size both enter the same port. What differs is the stud end itself. The ISO 6149-3 L series stud end is the light duty form and the ISO 6149-2 S series stud end is the heavy duty form, with a longer thread length and a longer body for the same thread size. The printed tables show it size by size: at M14X1.5 the L series length is 33 mm against 35.5 mm for the S series, at M16X1.5 it is 34 mm against 39.0 mm, and at M27X2 it is 45 mm against 55.5 mm. For an ISO 6149 adapter the port is the fixed item and the stud end is the variable, so the duty of the load case decides which form to specify.

The printed port note explained. The chart carries the note “Fit for ISO 9974-1 port or ISO 6149-1 port when useless of retaining ring.” It tells the buyer that this L series stud end is not restricted to one port standard: it mates with an ISO 9974-1 port as supplied, and it also mates with an ISO 6149-1 port when the retaining ring is not used. The sealing element is unchanged in both cases, because the O-ring on the stud end still seats in the recess of the port face and still does the sealing work; the note is about the retaining-ring detail at the port, not about a change of seal.

Make these three measurements before ordering:

1. Thread. Measure the outside diameter and the pitch, and record M14X1.5 rather than M14, because the pitch separates a metric stud end from a similar-looking thread of another family.
2. Seal type. Read the port, not only the part. A metric O-ring port has a machined recess; a 60° cone seat is a metal seat with no recess; a flat face for a bonded seal washer is plain.
3. Seat and duty. Record thread length A or B and overall length L, and establish whether the port expects the light duty or the heavy duty stud end, because length and duty together decide between the L series and the S series.

7. Ordering, Packaging and Delivery

To order, give the series code, the full part number, the thread size, the seal material, the body material and plating, and the quantity. A complete line reads: 1H adapter, part number 1H-14, M14X1.5 at both ends, O-rings in NBR, carbon steel with trivalent chromium zinc plating, 300 pieces. For an ISO 6149 adapter order, state whether the ports are ISO 9974-1 or ISO 6149-1 so the retaining-ring detail can be confirmed, and state any corrosive or offshore duty at the enquiry stage so the right material and seal compound are quoted in the same reply.

Packaging is arranged for two routes. For distributor shelves, these metric adapters are packed in labelled cartons marked with the part number, thread size and seal material so a box can be identified without opening it. For direct-to-line OEM delivery, parts are packed in bulk or in kitting trays for line-side handling, with the customer part number on the label alongside the HENGHUA number.

8. FAQ

What is the difference between a straight-thread O-ring seal and a tapered pipe thread?

A straight-thread O-ring joint, such as the 1H adapter in an ISO 6149-1 port, seals on an elastomer O-ring compressed in a machined recess in the port face, and the parallel thread only clamps the parts. A straight thread adapter therefore needs no sealant, while a tapered pipe thread seals by interference between the thread flanks plus a filler such as tape or paste. The exception to remember is that a tapered port cannot accept an O-ring, because it has no recess to hold one.

Can BSP and NPT be interchanged?

No. BSP and NPT are different thread families with different forms and flank angles, and they are not interchangeable even when the nominal sizes look close. The same applies to mixing a metric ISO 6149 port with an imperial BSPP port: both seal on a recessed O-ring, but the thread form and the recess dimensions differ, so the joint will not seal. The exception is a dedicated cross standard adapter made with one thread of each family; never force one thread into the other.

How do I identify the correct 1H adapter size?

Read the thread marking on the ports or measure it. The printed range covers M10X1, M12X1.5, M14X1.5, M16X1.5, M18X1.5, M22X1.5, M27X2, M33X2, M42X2 and M48X2, which correspond to the 1H-10 to 1H-48 part numbers. Measure the outside diameter and the pitch, match the pair to the table, then confirm thread length A and B and hex S1 so the part seats and stays accessible.

What is the difference between the metric L series and the metric S series?

Both use the same ISO 6149-1 port, but the stud ends differ. The L series is the light duty form and follows ISO 6149-3, while the S series is the heavy duty form and follows ISO 6149-2, with a longer thread length and a longer body for the same thread size. In the printed tables the L series is the 1H family and the S series is the 1H-H family. Select the duty that the port and the load case require, not the one that happens to be in stock.

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

NBR is the general-purpose choice for mineral hydraulic oil and covers approximately -30°C to +100°C. FKM suits higher temperatures and many aggressive fluids and covers approximately -20°C to +200°C. EPDM covers approximately -40°C to +120°C and is the usual choice for water-based fluids, but it is not suitable for mineral oil. Confirm the compound against the actual fluid and temperature before ordering.

How is the working pressure of this fitting determined?

The printed chart for the 1H series has no pressure column, so working pressure is confirmed per order by HENGHUA engineering, based on the thread size, sealing method and material selected. The reason is that on a straight-thread O-ring joint the capability is set by the port and the housing as much as by the hydraulic adapter. The rule is that the rating must be established against the actual port, material and duty cycle; the exception is that a larger thread size does not automatically permit a higher pressure in every housing.

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

Minimum order quantity is confirmed per order, because it depends on the size, the material and the plating selected. Sample pieces can be supplied before a production order so that both thread fits and both O-ring seatings can be checked against the real ports. Send the part number, thread size and seal material with the request so the sample is quoted in the correct configuration.

To close, HENGHUA invites your 1H adapter enquiry: send the part number, thread size, seal material, body material and quantity, and our engineering team will confirm the configuration, the stud end duty against your port, the working pressure for your housing, and the lead time for your order.

Related series in the same family: the 1H-H adapter and the 4H plug. Browse the full Hydraulic Adapters range for the complete ISO 1179 BSP, ISO 6149 metric, ISO 11926-3 SAE O-ring boss and SAE J513 cone families.