BS 1139 vs EN 74: How the Scaffold Coupler Standards Relate and What to Specify

“BS 1139” and “EN 74” are not two rival coupler standards. They are two names from one line of documents. BS 1139-2.1:1991 was the UK publication of the European standard EN 74:1988; EN 74:1988 was replaced by EN 74-1:2005, which was replaced by EN 74-1:2022, amended in 2025. The edition in force in the UK is BS EN 74-1:2022+A1:2025. A label such as “BS 1139 / EN 74” does not identify an edition — and the edition decides which test table the coupler was meant to pass.

Below: the editions in order, the 1988 table beside the current Table 8, what a type test involves, and the lines for a purchase order. We have not read EN 74-1:2005, and this article attributes no requirement value to it.

From BS 1139 to BS EN 74-1:2022+A1:2025, edition by edition

In 1991 the UK published the European standard under its own number. EN 74:1988 appeared as BS 1139-2.1:1991 — Part 2 (couplers), Section 2.1 of the BS 1139 Metal scaffolding series — so for that edition “BS 1139” and “EN 74” were the same requirements under two numbers. The current UK edition carries the European number: its national foreword calls BS EN 74-1:2022+A1:2025 the UK implementation of EN 74-1:2022+A1:2025, superseding BS EN 74-1:2022, which is withdrawn.

The class letters began as a bridge from the old British coupler. The EN 74:1988 foreword states that, for right-angle couplers, Class A is equivalent to the grade given in BS 1139-2:1982 and Class B is 50 % stronger than Class A; for friction-type sleeve couplers, the new Class B is equivalent to the British coupler in the earlier BS 1139-2 and Class A is 50 % weaker than Class B. So the old British coupler became Class A for a right-angle coupler and Class B for a sleeve coupler. The foreword uses “grade” for the 1982 British coupler and “class” for EN 74’s letters; on a current order, ask for a class.

The 2025 amendment is not cosmetic. Amendment A1 was approved by CEN on 10 February 2025, with national implementation by October 2025. Its one substantive tagged change is the slipping evaluation rule in clause 7.2.1.5, which takes the Δ2 slipping force as the lowest force measured between 1 mm and 2 mm of displacement. A test report written to EN 74-1:2022 before the amendment predates that tagged change, so ask which text a report was written to.

Some fittings sit outside the current Part 1. The introduction of BS EN 74-1:2022+A1:2025 places other less common coupler types in EN 74-2 and plain base plates and loose spigot pins in EN 74-3. We have obtained neither, which is why the girder coupler and joint pin guides carry no requirement table. The putlog coupler is not among the four types in Table 1 of BS EN 74-1:2022+A1:2025 either: Altrad Generation’s catalogue lists its putlog couplers (codes 26003 and 26126) to BS 1139-2.2:2009, not EN 74-1 (accessed 16 September 2026). We have not read BS 1139-2.2:2009 and publish nothing from it.

What changed between the 1988 table and Table 8

Both sets of figures below are prototype type-test requirements: the 1988 edition states that its requirements are for the assessment of prototypes, and the current figures are characteristic values, the 5 % quantile of the test results. Neither set is a safe working load.

Transcribed from Table 1 of BS 1139-2.1:1991 and Table 8 of BS EN 74-1:2022+A1:2025. Where the displacement criterion or the quantity differs, two cells are not old and new values of one requirement. Five things to read from it:

1. The Class A and B right-angle slipping and failure headline values match, which is why a 1988 figure and a current one look interchangeable. The second slipping limit is not measured the same way: under 0,5 mm of movement in 1988, the lowest force between 1 mm and 2 mm now.
2. The swivel gained classes. EN 74:1988 gave it one set of values; BS EN 74-1:2022+A1:2025 has Classes A and B, with the right-angle coupler’s slipping requirements class for class and a lower failure force (swivel coupler guide). A “Class A swivel” quoted against 6,0 / 8,5 / 17,0 kN mixes two editions.
3. The parallel coupler’s criteria moved. The 1988 limits sat at displacements under 2,0 mm and 0,5 mm; the current first limit allows up to 7 mm. A 1988 15,0 kN and a current 7,0 kN are not two values of one requirement.
4. The sleeve bending rows measure different things — a force in kN in 1988, a moment in kNm in the current edition. The sleeve coupler vs joint pin guide sets out why they cannot be compared.
5. Classes AA and BB belong to the current edition. In BS EN 74-1:2022+A1:2025, two identical AA or BB right-angle couplers positioned touching each other carry their own slipping requirement (double coupler guide); the 1988 table has Classes A and B only. And EN 74:1988 listed the shear-pin sleeve coupler (SS) and the loose spigot (LS); Table 1 of BS EN 74-1:2022+A1:2025 does not list them.

What these tables cannot tell you

They compare two endpoints. Between them sits EN 74-1:2005, which we have not read, so we cannot say whether a given difference arrived in 2005 or in 2022. What we can cite is the European foreword of EN 74-1:2022, which lists four changes against the 2005 edition:

1. reference tubes with the specified yield strengths were not procurable, so those requirements were changed;
2. new test conditions were specified;
3. the requirements for the bending moment of sleeve couplers were changed;
4. editorial changes were made.

The A1:2025 amendment’s one substantive tagged passage, the clause 7.2.1.5 evaluation rule described above, comes on top of those four. Anything beyond those five items about what changed, and when, is not in our sources.

What a type test under BS EN 74-1:2022+A1:2025 involves

Who does it. Clause 12 requires the assessment to be carried out by a person or organisation other than the coupler’s designer, and its note says requirements for assessment vary between countries. Under BS EN 74-1:2022+A1:2025, conformity is a third-party-assessed type test — not a CE mark, not a certificate for each batch. Our sources do not record what a UK or Gulf project authority requires, so ask the specifier which assessment the project accepts.

What is tested, and on what. For a right-angle coupler, Table 9 runs ten slipping tests on reference tube RTS1 (48,3 mm outside diameter, 3,2 mm wall, ReH ≥ 235 N/mm²) plus five on aluminium tube RTA, the failure and pull-apart tests on a solid steel bar RB, and the indentation tests on tube RTS2. Screw couplers are tightened to 50 Nm with a torque wrench, wedge couplers with a hammer of at least 500 g until the jarring blow; each coupler is tightened and untightened five times first, and the slip load goes on at least ten minutes after tightening. The results are analysed to EN 12811-3 for the 5 % quantile, which must not fall below the Table 8 value.

Production control after the type test. Annex B is informative — recommendations, not requirements. It describes two levels of ongoing production control: L, the manufacturer’s own quality control under EN ISO 9001 or a similar system, and M, the manufacturer’s control supervised by an independent certification system, with the annex describing third-party control as taking place twice a year in the normal case. Its Table B.2 sets the internal test frequency at one slipping and failure test per 50 000 couplers, minimum one per week, for right-angle and swivel couplers, and one per production run for parallel and sleeve couplers; a third-party inspection takes five right-angle or swivel couplers, or two parallel or sleeve couplers. A buyer who wants level M has to write it into the order.

The product manual. Clause 13 requires a manual stating, among other things, the coupler type and class, the identity of the assessor with a copy of the assessment statement, the 48,3 mm tube types permitted and the 50 Nm torque or the hammer. Because it names the assessor, it is a good first document to ask a supplier for.

What “BS 1139” means when it appears on a specification or supplier page

“BS 1139 couplers” on a tender, specification or purchase order can mean several things, and the words alone do not say which. One possible meaning is the superseded edition; on the supplier pages in our sources (accessed 16 September 2026) the name also appears in three other ways:

• As the superseded edition. The writer may mean BS 1139-2.1:1991, that is EN 74:1988; a report to it is a report against the 1988 table above.
• As a combined label. Dura Scaffold labels its British-type double and swivel couplers “BS1139/EN74” — a label naming both, with no edition.
• As a different BS 1139 document. Altrad Generation lists its putlog couplers to BS 1139-2.2:2009, and London Scaffolding Supplies lists board retaining clamps as “BS 1139” while listing its sleeve, swivel and pressed-steel double couplers to BS EN 74-1.
• Beside an edition year. Altrad Generation lists its doubles and swivels, and Gilray its double coupler, to the 2005 edition of EN 74-1. That tells you what the catalogue says; it does not tell you what that edition required, which we have not read.

When a document you have to price or supply says only “BS 1139”, use these three questions to clarify it:

1. Which document and edition does the specifier mean? Ask in writing. If it is the current edition, the line becomes a designation such as EN 74-1 RA B C2 M with BS EN 74-1:2022+A1:2025 named beside it.
2. Which type and class at each joint? The class is a design input: it comes from the designer, not from the supplier or from us. Class letters are type-specific, so the doubles’ class says nothing about the swivels’ or sleeves’.
3. Which fittings fall outside the four BS EN 74-1:2022+A1:2025 types? For putlog couplers, board retaining clamps, beam couplers and joint pins, keep the document the specification names and ask the supplier for the test basis of the exact product; the clause 8 designation in BS EN 74-1:2022+A1:2025 has no type code for them.

If the specifier does mean BS 1139-2.1:1991, note that it is superseded; whether the project accepts a report against the 1988 table is the specifier’s decision. What should not happen is a silent swap of one name for the other in a contract: the Class A and B right-angle slipping and failure headline values match, but the swivel classes, the parallel criteria, the sleeve bending row and the Δ2 rule do not.

Reading the mark: what it tells you and what it does not

Clause 9 of BS EN 74-1:2022+A1:2025 requires every coupler to be marked by impressing or embossing on the flap or the body, legible after the protective coating has been applied, with characters at least 4,0 mm high and 0,2 mm deep. The sequence is the reference EN 74-1, the manufacturer’s registered trademark, the last two digits of the year of manufacture, the coupler class, the type of ongoing production inspection if provided, and optionally the customer’s name or logo. The standard’s example is EN 74-1 XX 21 BB M; NASC TG17:10 records the same scheme as EN74-1 xx 05 A L (walk-through in the coupler types guide).

What the mark does not carry is the edition. The two digits are the year of manufacture — the 21 in the standard’s example and the 05 in NASC’s are years the fitting was made — so a mark cannot tell you whether the coupler was type-tested to the 2005 text, the 2022 text or the 2022 text as amended in 2025. The type-test report has to. A mark without a class letter does not identify a class, and a coupler cast to the Chinese GB 15831-2006 — withdrawn on 1 December 2023 and replaced by GB/T 15831-2023, which we have not read — carries a year, a trademark and a model designation with no class letter at all, because the 2006 edition has no class system.

What to write on the order and what to ask the supplier for

1. The edition and the designation, for each coupler type. Clause 8 sets the designation as EN 74-1 <type> <class> <corrosion class> <inspection level>: type RA, SW, PA or SF; class A, AA, B or BB for a right-angle coupler, A or B for the others; corrosion class C1, C2 or C3 (electrolytic zinc of 15 µm average thickness conforms to C2); and an inspection letter — the format allows L, M or X, and Annex B describes L and M. A complete line reads:

Double coupler (right-angle), BS EN 74-1:2022+A1:2025, EN 74-1 RA B C2 M

and the swivels on the same order get their own line, for example EN 74-1 SW B C2 M. “EN 74”, “EN 74 clamp” or “BS 1139” alone identifies neither an edition nor a class.

2. The type-test report, with six items checked. Ask for the report for the type and class you are ordering — not the factory’s report for a different coupler — and check that it shows:

• the assessor: who carried out the assessment, and that they are independent of the coupler’s designer (clause 12);
• the report number, recorded for traceability;
• the edition it was written to: BS EN 74-1:2022+A1:2025, the unamended 2022 text, or an earlier one;
• the type and class tested, matching the designation on your order;
• the date of the test and of the assessment;
• the tightening torque: 50 Nm for screw couplers under BS EN 74-1:2022+A1:2025. 40 N·m is the test torque of GB 15831-2006 (withdrawn on 1 December 2023, replaced by GB/T 15831-2023), so a sheet run at 40 N·m was not run to the BS EN 74-1:2022+A1:2025 test condition.

3. L or M, chosen on purpose. Level L is the manufacturer’s own control; level M adds supervision by an independent certification system. If you want M, write it into the designation and ask for the most recent third-party inspection report; Annex B describes level M but, as an informative annex, does not require it.

4. A marking check on a sample. Before the order ships, check on a sample that the EN 74-1 mark is present, that the class letter matches the line on the order, and that the characters are legible after galvanising.

5. The tube. State 48,3 mm outside diameter and the wall thickness of the tube the couplers will go on. Do not copy 3,2 mm across as a minimum: in the current edition it is the wall of reference test tube RTS1, and it was EN 74:1988 that wrote 3,2 mm into its own scope.

Also specify the applicable finish, fastening method, forged or pressed construction and quantity; those lines are covered in the eight-point purchase-order list in the coupler types guide.

GB 15831 and AS/NZS 1576.2 are not other names for EN 74

China. GB 15831-2006 《钢管脚手架扣件》 (steel tube scaffold couplers) states in its foreword that it referred to ISO 4054:1980 — not to EN 74 — and it has no class system: a designation such as GKZ48A GB 15831—2006 identifies a right-angle coupler (code Z) for the standard’s 48.3 mm tube (main-parameter code 48) and says nothing about an EN class. Its tests run at 40 N·m bolt torque on a 48.3 × 3.5 mm red-lead-painted tube. BS EN 74-1:2022+A1:2025 tightens screw couplers to 50 Nm, and for a right-angle coupler runs its slipping tests on reference tubes RTS1 and RTA, failure and pull-apart on bar RB and indentation on tube RTS2 — so a GB 15831-2006 test sheet is not a BS EN 74-1:2022+A1:2025 type-test report. It was withdrawn on 1 December 2023 and replaced by GB/T 15831-2023, which we have not read; GB (mandatory) became GB/T (recommended). Its figures are in the double coupler guide.

Australia and New Zealand. AS/NZS 1576.2:2016 clause 1.6 deems couplers that have demonstrated conformity with the performance requirements of EN 74-1:2005 for Class B right-angle and Class A swivel couplers to comply without further testing, where those requirements are equivalent to its own, subject to assessment against its dimensional requirements. It names that one edition and those two type-and-class combinations only, and it does not make the EN editions interchangeable with each other.

Send a coupler specification written as a designation, with the edition and the class for each coupler type.

Frequently asked questions

▸Is BS 1139 the same as EN 74?

Not as a current standard. BS 1139-2.1:1991 was the UK publication of EN 74:1988, which is superseded: EN 74:1988 was replaced by EN 74-1:2005, which was replaced by EN 74-1:2022, amended by A1:2025. The coupler standard in force in the UK is BS EN 74-1:2022+A1:2025, the UK implementation of EN 74-1:2022+A1:2025. Separately, Altrad Generation's catalogue lists its putlog couplers to BS 1139-2.2:2009 (accessed 16 September 2026), a document we have not read.

▸What is the current scaffolding coupler standard?

In the UK it is BS EN 74-1:2022+A1:2025, which supersedes BS EN 74-1:2022 (withdrawn). It covers four types of friction coupler for 48,3 mm steel and aluminium tube: right angle (RA), swivel (SW), parallel (PA) and sleeve (SF). Its introduction places other less common coupler types in EN 74-2 and plain base plates and loose spigot pins in EN 74-3.

▸What does Class B mean on a double coupler?

It depends on the edition and the coupler type. In BS EN 74-1:2022+A1:2025, Table 8 requires a Class B right-angle (double) coupler prototype to reach a characteristic slipping force of 10,0 kN at Δ1 ≤ 7 mm and 15,0 kN at 1–2 mm displacement, a failure force of 30,0 kN and a pull-apart force of 30,0 kN, plus rotational and cruciform-bending requirements for screw couplers that Class A does not carry. These are type-test values, not working loads. A Class B swivel coupler has a different set of requirements.

▸What is the load capacity of an EN 74 coupler?

Table 8 of BS EN 74-1:2022+A1:2025 is not a load capacity table. It sets characteristic type-test values, the 5 % quantile of prototype test results, and clause 6.2.1 sends the reader to EN 12811-1 and EN 12812 for the values and safety coefficients to apply in use. The working load comes from the scaffold design. A slip-resistance figure printed by a UK distributor, such as TRAD UK's 6.10 kN for its Class A drop-forged double coupler (accessed 16 September 2026), is that supplier's own stated figure; the listing does not establish an allowable working load.

▸What should an EN 74 coupler order say?

The edition and the clause 8 designation for each coupler type, for example 'Double coupler, BS EN 74-1:2022+A1:2025, EN 74-1 RA B C2 M'. Ask for the type-test report for that type and class, showing the assessor, the report number, the edition it was written to and the date, and check the EN 74-1 mark and class letter on a sample.

Sources

1. BS EN 74-1:2022+A1:2025 Couplers, spigot pins and baseplates for use in falsework and scaffolds — Part 1: Couplers for tubes (current edition; national and European forewords, introduction, clause 1, Tables 1, 2, 7, 8 and 9, clauses 6.1, 6.2.1, 6.2.3, 7.1.7–7.1.10, 7.2.1.5, 8, 9, 12, 13, Annex B). BSI product page — accessed 2026-09-17
2. BS 1139-2.1:1991 (EN 74:1988) Metal scaffolding — Part 2: Couplers — Section 2.1: Specification for steel couplers, loose spigots and base-plates. Superseded; cited for its scope, foreword class definitions, coupler codes and Table 1 type-test limits. Current edition sold by BSI — accessed 2026-09-16
3. NASC TG17:10 Identification of BS EN74 Scaffold Fittings (January 2010) — NASC official website — accessed 2026-09-16
4. NASC TG17:10 — copy seen at a supplier mirror (Wellmade, China). A vendor mirror, not an authoritative host; cited only to show the copy consulted — accessed 2026-09-16
5. AS/NZS 1576.2:2016 Scaffolding — Couplers and accessories (clause 1.6). Standards New Zealand product page — accessed 2026-09-16
6. GB 15831-2006 《钢管脚手架扣件》 Steel tube scaffold couplers — withdrawn 2023-12-01, replaced by GB/T 15831-2023. Official catalogue record, 全国标准信息公共服务平台 — accessed 2026-09-16
7. Altrad Generation — Scaffold fittings catalogue (putlog couplers 26003 and 26126 listed to BS 1139-2.2:2009; doubles and swivels listed to BS EN 74-1:2005) — accessed 2026-09-16
8. Gilray — Double couplers, listed to EN 74-1:2005 Class B — accessed 2026-09-16
9. Dura Scaffold — EN74 British forged scaffolding couplers (fittings marked 'BS1139/EN74') — accessed 2026-09-16
10. London Scaffolding Supplies — Scaffold fittings (couplers listed to BS EN 74-1, board retaining clamps to BS 1139) — accessed 2026-09-16
11. TRAD UK — Double coupler product listings (supplier's stated slip resistance and class) — accessed 2026-09-16