Half coupler

A coupler with only one jaw for a 48.3 mm tube; the other side is welded to a component or ends in a threaded bolt for fixing to steel or timber.

Also called: single coupler, weld-on coupler, bolt-on coupler, half clamp

Not every part of a scaffold is a tube. Brackets, bridging beams, stair handrails or fan arms still have to sit firmly on an upright. The half coupler does this: it has just one jaw for a 48.3 mm tube. The other side is either welded to a component or ends in a threaded bolt for fixing to steel sections, timber or special parts.

You often meet it without noticing. The inside bracket of a frame scaffold is frequently fixed to the upright with a welded half coupler, as are some outside brackets and bridging beams. Handrails of landing stairs also usually arrive with half couplers already fitted.

Variants

The clamping side is like half a right-angle coupler – one jaw, a hinged cap, a bolt with nut, normally a 22 mm spanner. The back is what differs.

• Weld-on half couplers are fixed to brackets, beams, deck locks or ledgers. They are not bought separately but are part of the component.
• Half couplers with threaded bolt, often M20 in various lengths, bolt onto sections, plates or anchor assemblies. The nut on the thread side may need a different spanner from the jaw.
• Half couplers with drop-lock pin take guard rails or diagonals of frame scaffolds.

Such special couplers are covered by EN 74-2. In practice that means each half coupler carries only what its manufacturer has verified – and what the part it hangs on can take.

Fitting

1. Inspect part and coupler: weld free of cracks, cap straight, thread running.
2. Hold the component at its intended point on the upright – for brackets usually right at the node below the deck bearing.
3. Close the jaw round the tube and run the nut down by hand.
4. Align position and height so decks lie level without gaps.
5. Tighten to 50 Nm; on bolt-on types tighten the thread side as well.
6. Check visually and add any further locking required, such as a pin, strut or deck lock.

When dismantling, take decks and loads off the component before releasing the coupler. A bracket hanging only by its clamp should never be left unattended.

What to look out for

• Welds are the weak point: hairline cracks where the coupler joins bracket or beam mean rejection.
• No welding on site: a coupler welded on afterwards has no verification and can weaken the part, and the heat damages the zinc.
• Right tube: the jaw fits only 48.3 mm tube to standard.
• Threaded bolts must not be bent or overloaded with extensions.
• Low torque lets brackets sag – a real risk with wide decks.
• Buying used brackets or beams: always check the half coupler too – free bolt, straight cap, no weld cracks, no thick concrete in the jaw.

Whether a half coupler suffices at a given point or a full coupler is needed is decided by the system instructions. Used couplers are listed under couplers.