Scaffolding Coupler Types and Names: UK, US and EN 74 Chart

A scaffold coupler is a fitting that joins scaffold tube to scaffold tube — or, in the case of the beam clamp, tube to a steel beam; the four types BS EN 74-1:2022+A1:2025 specifies are for 48,3 mm outside-diameter tube. In the UK, the standards and the trade call it a coupler; in the US and in general speech it is a clamp. Same object, same job. This guide covers the coupler types you will find on a tube-and-fitting scaffold, the standards they are made and marked to in the UK, Europe, the US and Australia, and the load figures those standards actually require, with each figure traced to its source.

Coupler types at a glance

The first six are the ones that matter on a purchase order. Board retaining and half couplers are accessories. How these fittings sit in a finished scaffold — standards, ledgers, transoms, braces and ties, with the US and UK name for each — is set out in tube and clamp scaffolding explained.

Double coupler (right-angle clamp)

The workhorse. It holds two tubes at a fixed right angle and carries the vertical load from a ledger or transom into a standard. Every load-bearing connection in a basic tube-and-fitting scaffold that is not a brace uses a double coupler. It is the fitting the standards test hardest, and the only one for which a UK purchase order routinely specifies a class.

UK trade practice is to call it a double; EN 74 calls it a right-angle coupler (RA); US suppliers call it a right-angle clamp or 90-degree clamp. Drop-forged and pressed-steel versions both exist and both can be certified to EN 74-1.

Swivel coupler (swivel clamp)

Two halves joined by a rivet so the tubes can be locked at any angle. Used for diagonal bracing, ledger bracing and anywhere the geometry is not 90°. Because the rivet is a moving part the swivel coupler has its own test regime in every standard, and its rated loads are lower than a double coupler’s.

Sleeve coupler (external joint)

Joins two tubes end to end from the outside. BS EN 74-1:2022+A1:2025 lists it as the sleeve coupler, type SF, the type for tubes joined end to end coaxially, and its Table 8 sets it a slipping force in both classes and, for Class B, a bending moment. EN 74:1988 distinguished a friction sleeve coupler (SF) from a sleeve coupler with shear pins (SS); Table 1 of BS EN 74-1:2022+A1:2025 does not list SS.

Joint pin (spigot, coupling pin)

A joint pin is the internal form of an end-to-end tube joint. BS EN 74-1:2022+A1:2025 does not cover it: its scope is right angle, swivel, sleeve and parallel couplers working by friction, and its introduction places loose spigot pins in EN 74-3, which we have not obtained. No standard in our source ledger records a tensile or bending requirement for a spigot pin, so where one may be used is a question for the scaffold design and for the applicable type-test report the supplier provides. Sleeve couplers and joint pins are compared in their own guide.

Putlog coupler (single clamp)

A single flap and bolt that fixes a putlog or transom to a ledger. It is not a load-bearing coupler in the standards’ sense; UK suppliers list it against BS 1139-2.2 rather than EN 74-1, and AS/NZS 1576.2 tests it at a fraction of the force applied to a double coupler.

Beam clamp (girder coupler)

Joins a scaffold tube to the flange of a steel beam rather than to another tube. BS EN 74-1:2022+A1:2025 does not list it among the four coupler types in its Table 1, and no standard or supplier page in our source ledger gives a load value for it, so any rating has to come from the product’s own type-test report and the scaffold design. What to ask a supplier instead is in the beam clamp and girder coupler guide.

Standards: what “BS 1139” and “EN 74” mean today

The names buyers use for coupler standards have shifted three times, and an order that says only “BS 1139” is ambiguous.

EN 74:1988 applied to “steel tubes of 48,3 mm outside diameter and of at least 3,2 mm nominal wall thickness”. Its foreword defined the classes in a way that still trips buyers up: for right-angle couplers “Class B is 50 % stronger than Class A”, but for friction-type sleeve couplers “the new Class B is equivalent to the British coupler in the earlier BS 1139-2 and the Class A is 50 % weaker than Class B”. So Class B is the higher class in both cases, but the letters were fixed by history, not by a single scale, and the class of a double coupler says nothing about the class of a sleeve coupler from the same factory.

How to read the marking

NASC guidance note TG17:10 explains the marking that EN 74-1 requires on every coupler, embossed on the flap in characters at least 4.0 mm high and 0.2 mm deep, in this order: the standard reference, the maker’s trademark, the last two digits of the year of manufacture, the class letter, and the inspection level. The example given is EN74-1 xx 05 A L. Inspection level L means production control by a manufacturer approved to ISO 9001 or similar; M means the control is supervised by an independent certification body. A coupler with no class letter cannot be sold as EN 74-1 compliant.

United States: OSHA 29 CFR 1926.452(b)

The US has no product standard equivalent to EN 74-1. OSHA regulates the scaffold, not the coupler, through 29 CFR 1926.452(b). Couplers “shall be of a structural metal, such as drop-forged steel, malleable iron, or structural grade aluminum”, and “the use of gray cast iron is prohibited”. Transverse bracing is required at the scaffold ends, at least at every third set of posts horizontally and every fourth runner vertically. Tube and coupler scaffolds over 125 feet (38 m) must be designed by a registered professional engineer. The general rule in 1926.451(a)(1) applies to every component: it must support its own weight and at least 4 times the maximum intended load. OSHA’s fact sheet FS-3760 gives the duty ratings of 25, 50 and 75 lb/ft² for light, medium and heavy-duty scaffolds.

Australia and New Zealand: AS/NZS 1576.2:2016

AS/NZS 1576.2:2016 tests a right-angle coupler by applying a vertical force of 12.5 kN and holding it for one minute; the coupler must not slip more than 6 mm. Where a screw-tightened coupler is tested for a higher slip resistance, “the test load shall be twice the intended WLL”. A check coupler must have a working slip resistance of at least 9 kN. Clause 1.6 of the standard states that couplers tested to EN 74-1:2005 as Class B right-angle couplers and Class A swivel couplers are deemed to comply without further testing, which is the cleanest published equivalence between the European and the Australian regimes.

Load ratings: type-test limits and safe working loads are different numbers

Every load figure you will see for a coupler is one of two things. A type-test limit is the force a prototype had to reach on a test rig before the design could be certified. A safe working load (SWL) is what a supplier or a design guide allows you to put on the coupler in service, after a safety factor. Suppliers’ catalogues quote SWLs; the standards’ tables quote test limits. The two sets of numbers below are shown side by side because they are usually mixed up. Other guides on editions, classes and load figures are collected under standards and load ratings.

What BS EN 74-1:2022+A1:2025 requires (current edition)

The current edition covers four coupler types — right angle (RA), swivel (SW), parallel (PA) and sleeve (SF) — and for right-angle couplers it recognises four classes: A, AA, B and BB. Its slipping requirement is tested at two displacements. Fs,c at Δ1 is the force the coupler must hold with a displacement of no more than 7 mm; Fs,c at Δ2 is the force at small movement, which amendment A1:2025 redefined as the lowest force measured between 1 mm and 2 mm of displacement. Every figure in the table is a characteristic value — the 5 % quantile of the type-test results — and is a requirement placed on a prototype, not a load you may apply on site.

Transcribed from Table 8 of BS EN 74-1:2022+A1:2025. A dash means the standard sets no requirement for that combination. Class B and BB right-angle couplers carry further requirements the table does not show — a rotational moment of 0,13 kNm, a rotational stiffness of 7,5 kNm/rad and cruciform bending stiffnesses — all of which apply to screw couplers only; Class B sleeve couplers must also reach a bending moment of 1,4 kNm. The shear-pin sleeve coupler (SS) and the loose spigot of the older edition are no longer part of EN 74-1. Screw couplers are tightened to 50 Nm with a torque wrench for the test, wedge couplers with a hammer of at least 500 g.

The AA and BB classes are the part most worth reading twice. Used on its own, an AA coupler has the same slipping and pull-apart requirements as an A and a BB the same as a B; only the failure force is higher. Their purpose is the pairing rule: two identical AA couplers positioned touching each other must reach 15,0 kN at Δ2 instead of 10,0 kN, and a BB pair 25,0 kN instead of 15,0 kN. That is a design option for a scaffold that needs more slip resistance at a joint, not a free upgrade to a single coupler.

Most supplier sites — including many whose product pages say “EN 74-1” — still quote the 1988 or BS 1139-2.1 figures. Part of the reason is that the numbers everybody repeats did not move: 10,0 kN and 15,0 kN for Class A and Class B right-angle couplers at the tighter displacement are the same in both editions, so nobody had a visible reason to re-check. What did move is everything around them. The displacement criterion changed (EN 74:1988 measured the slipping load at under 0,5 mm of movement; the current edition takes the lowest force between 1 mm and 2 mm). The swivel, parallel and sleeve values changed. The AA and BB classes did not exist in 1988. And the 1988 table circulated freely for thirty years in catalogues and training material, while the current text is sold only by BSI and CEN.

What EN 74:1988 required of a prototype (superseded, kept for comparison)

The figures below are transcribed from Table 1 of BS 1139-2.1:1991, the UK edition of EN 74:1988. That edition is superseded and should not be written on a new order. It is set out here because it is the table most catalogues, training notes and vendor pages still reproduce, and because the class structure it created is the one stamped on fittings already in circulation.

The 1988 edition had no class split for swivel, shear-pin sleeve or parallel couplers. Where a supplier catalogue quotes a “Class A swivel” or “Class B swivel”, it is using the later scheme; the current values for those classes are in the 2022 table above. Note also that the shear-pin sleeve coupler (SS) row has no counterpart today — that type left EN 74-1 with the 2022 edition.

What UK suppliers quote today

UK distributors sell double couplers with the safe working load printed in the listing. TRAD UK lists a drop-forged double coupler as “BS EN 74-1 Class A” with a slip resistance of 6.10 kN, and a pressed-steel double coupler as “BS EN 74-1 Class B” with 9.10 kN (both accessed 16 September 2026). The 6.1 kN and 9.1 kN pair is the figure UK scaffolders quote for doubles, and it is consistent with the 50 % step between classes that EN 74:1988 defined. It is a supplier’s working-load figure, not a number printed in a standard we have been able to read.

Chinese exporters tend to quote the test-limit figures instead. Wellmade, a Chinese manufacturer, lists its EN 74 Class B forged double coupler with a slipping force of “more than 15 kN” and a failure load of “more than 30 kN”, which are the Class B right-angle values from the EN 74 test table. Read a Chinese quotation with that in mind: “15 kN” on a Class B double from a factory and “9.1 kN” on the same coupler from a UK stockist are describing the same product with two different numbers.

Drop-forged or pressed steel

Both are legitimate and both can carry an EN 74-1 Class B mark; the same UK distributor sells a drop-forged Class A double and a pressed-steel Class B double. Drop-forged couplers are made from a heated steel billet hammered into a die, and are heavier and thicker in the flap. Pressed couplers are cut and folded from sheet, lighter and cheaper. Which one a market expects is a matter of local habit and of the buyer’s specification, not of the standard. The full comparison, including what each process means for galvanising and for service life, is in its own guide.

Weights for freight planning

Figures are the vendors’ catalogue weights, accessed 16 September 2026; our ledger records a 48.3 mm tube size against the double and swivel rows, and no tube size against the girder coupler. Where only one vendor is listed the weight is that vendor’s, not a market typical. Forged doubles for mixed tube sizes go up quickly: Wellmade lists 1.45 kg for 60 × 48 mm, 1.60 kg for 60 × 60 mm and 2.35 kg for 89 × 48 mm.

Tightening torque

AS/NZS 1576.2:2016 states that for a screw-tightened coupler “a torque of 54 Nm shall be sufficient for the coupler to satisfy the requirements of Section 4”, and that couplers must withstand at least 80 Nm without permanent distortion. Altrad Generation quotes approximately 50 Nm for its drop-forged swivel coupler. EN 74-1 has its own tightening procedure for type tests; ask the factory which torque its test report was run at.

What to put on the purchase order

1. Tube size. The outside diameter and wall thickness of the tube in use. The four BS EN 74-1:2022+A1:2025 types are for 48.3 mm outside-diameter tube, with walls such as 3.2 mm Type 3 or 4.0 mm Type 4 to BS EN 39; our ledger records no tube size for the girder coupler, so confirm it with the supplier for the exact product. Couplers for other tube diameters and for mixed sizes exist but are different products — if your tubes are not 48.3 mm, confirm the size with the supplier before ordering.
2. Type and quantity per type, using the UK or EN name and, for a US buyer, the US name in brackets.
3. Standard edition and class for each type the cited standard classifies (BS EN 74-1:2022+A1:2025 classifies none of the beam clamp, putlog or joint pin; see the girder coupler guide for what to ask instead): for example “double coupler, BS EN 74-1:2022+A1:2025, Class B”.
4. Forged or pressed.
5. Finish: electro-galvanised (zinc plated), hot-dip galvanised or painted, and the coating thickness if it matters to you.
6. Marking: for the EN 74-1 types, ask for the EN 74-1 mark with class letter and inspection level on every piece, and check the marking on a sample against TG17:10.
7. Test evidence: a type-test report from a named laboratory, to EN 74-1 for the types it covers and to a named document for any other fitting, dated and matching the design you are buying, not a certificate for a different coupler from the same factory.
8. Bolt grade: Wellmade specifies grade 8.8 bolts on its forged doubles; ask what grade your supplier fits.

Use this checklist to start a coupler enquiry, then see how to order.

Sources

1. BS 1139-2.1:1991 (EN 74:1988) Metal scaffolding — Part 2: Couplers. Superseded; cited for its Table 1 type-test limits. Current edition sold by BSI — accessed 2026-09-16
2. 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, BSI product page) — accessed 2026-09-16
3. 29 CFR 1926.452(b) Tube and coupler scaffolds (Cornell LII) — accessed 2026-09-16
4. OSHA Fact Sheet FS-3760, Tube and Coupler Scaffolds — Planning and Design (11/2014) — accessed 2026-09-16
5. AS/NZS 1576.2:2016 Scaffolding — Couplers and accessories (Standards New Zealand product page) — accessed 2026-09-16
6. NASC TG17:10 Identification of BS EN74 Scaffold Fittings (January 2010; copy seen on a supplier mirror, original at nasc.org.uk) — accessed 2026-09-16
7. TRAD UK — Double coupler product listings (drop forged Class A, pressed steel Class B) — accessed 2026-09-16
8. Gilray — Double couplers EN 74-1 Class B — accessed 2026-09-16
9. Altrad Generation — Drop forged swivel coupler — accessed 2026-09-16
10. Wellmade — Forged double coupler (EN 74 Class B) product page — accessed 2026-09-16
11. Altrad Generation — Scaffold fittings catalogue (codes, weights, standards) — accessed 2026-09-16
12. WCT Scaffold — Drop forged swivel coupler (EN 74-1 Class A) — accessed 2026-09-16
13. Dura Scaffold — EN74 British forged scaffolding couplers — accessed 2026-09-16
14. Scaffolding Direct — 48.3 mm x 4 mm galvanised scaffold tube, BS EN 39:2001 — accessed 2026-09-16