42.4 mm tube (Size C) has a smaller outside diameter and is lighter, while 48.3 mm tube (Size D) is stronger and standard for handrails and structural guardrails. Both are nominal-bore steel tube: 42.4 mm corresponds to 1¼" NB and 48.3 mm to 1½" NB. They are not interchangeable — fittings and tube must share the same size.

Yes, galvanised steel tube is suitable for outdoor and permanent use because the zinc coating protects the steel against rust in wet and exposed conditions. It is widely used for external handrails, railings, fences and scaffold-style frames. Hot-dip and pre-galvanised finishes both give long service life outdoors.

Yes, steel tube can be cut to length with a hacksaw, pipe cutter or angle grinder, and key clamp systems are designed for on-site cutting. Deburr the cut end and, for galvanised tube, treat the bare edge with zinc paint to maintain corrosion protection. Cutting does not affect how fittings clamp, as they grip the outside of the tube. GeZu Impex offers tube cut to size.

The load a key clamp steel tube structure carries depends on tube diameter, wall thickness, span and how it is supported, so figures vary by design. 48.3 mm (Size D) tube is typically specified for handrails and guardrails because of its greater strength, while shorter spans and closer supports increase capacity. For guardrail duty, follow the span and post spacing recommended for the system.