Fittings
What is a putlog coupler?
A putlog coupler fixes a transom or putlog to a ledger at right angles. It is a single coupler, not rated to carry the load a double coupler carries.
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<img src="https://scaffoldoptix.co.uk/glossary/putlog-coupler/diagram.svg" alt="putlog coupler — scaffold diagram from ScaffoldOptix" width="880" height="620" loading="lazy">
<figcaption>
<a href="https://scaffoldoptix.co.uk/glossary/putlog-coupler">What is a putlog coupler?</a> — diagram by
<a href="https://scaffoldoptix.co.uk">ScaffoldOptix</a>
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</figure>It exists because not every connection needs the duty of a double. A board-bearing transom sitting on a ledger transfers a modest load, and a lighter fitting is adequate for it.
The name comes from putlog scaffolds, where the horizontal member has one end built into the wall. The coupler is still used on independent scaffolds for intermediate transoms.
The failure mode is substitution in the wrong direction: a putlog coupler used at a connection that needed a double, usually because the box on the wagon was closer.
What goes wrong on site
- Used where a double coupler is required, which downgrades a structural connection.
- Used to fix bracing, which needs a swivel.
- Assumed to be interchangeable with a double because both join tubes at right angles.