Box Bar Sizes and Gauges Explained

Short answer: the section size decides how stiff the bar is; the wall thickness decides how much load it carries and how long it lasts outdoors. Window grilles take 3/4 or 1 inch in a light gauge; gates take 1½ or 2 inch at 1.4–1.6 mm; structural frames and posts take 2 × 2, 3 × 3 or 4 × 2 inch at 1.6–2 mm.

What the two numbers mean

Box bar is written as section × section – wall thickness, for example 1½ × 1½ – 1.6 mm. The first two numbers are the outside dimensions in inches. The last one is how thick the steel wall is, in millimetres.

• Going up a section size makes the bar much stiffer across a span. Stiffness rises very quickly with depth, so a deeper section does more to stop a gate sagging than a thicker wall does.
• Going up a gauge makes it stronger at the joints, heavier to handle, and far slower to rust through.

Choosing by the job

All of these sizes are stocked in the Iron & Metal section.

Rust is the real enemy in Sri Lanka

Humidity, monsoon rain and — near the coast — salt air all shorten the life of untreated mild steel. Two things decide how long a gate lasts:

1. Wall thickness. A 0.9 mm wall simply has less metal to lose than a 1.6 mm one. That is why a light gate rusts through at the bottom rail first.
2. Sealing the ends. Water gets inside hollow section through open ends and unsealed welds, and rusts it from the inside out where nobody can see it. Cap or weld the ends closed.

Then prepare and paint it. A wire brush, a primer and two coats will add years to a gate for very little money — and painting over loose rust simply lifts with the old coat.

Cutting and welding

• Cut it with an abrasive cutting disc, not a diamond or tile wheel — see our guide to which disc for which job.
• Light gauges (0.7–0.9 mm) burn through easily. Keep the current down and tack rather than running long beads.
• Grind the welds back before painting. Paint over slag lifts within a season.

Buying box bar

Box bar is cut and sold by the length and goes by lorry rather than courier. Send your cutting list through Request a Quote or call us and we will price the whole order delivered.

Common questions

What size box bar should I use for a gate?

For a normal house gate, use 1½ × 1½ inch or 2 × 2 inch at 1.4 to 1.6 mm for the frame, with a lighter section for the infill. Heavier gates and wide spans need 2 × 2 inch at 2 mm.

What does the mm number in box bar mean?

It is the thickness of the steel wall. Roughly: 0.7–0.9 mm is light, 1.1–1.2 mm is general purpose, 1.4–1.6 mm is strong, and 2 mm is heavy structural.

Why does box bar rust from the inside?

Water gets in through open ends and unsealed joints and sits inside the hollow section, where it cannot dry out and nobody can see it. Sealing the ends is what prevents it.

Which is better, a bigger section or a thicker wall?

For stopping sag over a span, a bigger section. For strength at the joints and for life outdoors, a thicker wall.

Need help choosing? Call +94 71 302 4843, message us on WhatsApp, or send your list through Request a Quote. WPL Trading, No. 305, Kandy Road, Dummaladeniya, Warakapola — open every day, 9.00 a.m. to 6.30 p.m., with island-wide delivery.

සිංහලෙන්: Box bar size එකයි gauge එකයි