Standard scaffolding couplers fit tube with a 48.3 mm outside diameter, which is the common scaffold tube size. Some couplers are made for 42.4 mm tube or offer an interface fitting to connect 48.3 mm and 42.4 mm tubes together. Always check the coupler's stated tube diameter so it clamps securely without slipping.

Scaffold couplers are usually made from drop-forged steel or pressed steel and finished with hot-dip galvanising or zinc plating for corrosion resistance. Drop-forged couplers are stronger and preferred for structural, load-bearing connections, while pressed couplers suit lighter duties. The galvanised finish lets them stay outdoors on site through wet weather without rusting.

Use a right-angle (double) coupler to join two scaffold tubes at a fixed 90-degree angle, because it is load-bearing and transfers weight between the tubes. Swivel couplers are for connecting tubes at any other angle, such as diagonal braces, and are not designed to carry the main load. For end-to-end extensions, use a sleeve coupler or joint pin instead.

Scaffolding couplers are tightened with a podger spanner or ratchet on the coupler bolt, usually a 22 mm hexagon nut. The recommended tightening torque is typically around 50 Nm, enough to grip the tube firmly without crushing it. Check that the coupler is square on the tube and fully seated before final tightening, and re-check bolts as the structure is loaded.