Choosing a rod diameter.
1.6, 2, 2.2, 2.5, 3, 3.15 and 4 mm. The choice is set by the thinnest part of the joint and the torch you have, not by the thickest section on the drawing.
Match the thinnest side.
The most common error in aluminium brazing is picking the rod to suit the heavy part of the joint. It is the wrong way round.
A larger rod needs more heat before it melts. If the joint includes thin-wall tube, getting a 4 mm rod flowing means putting more heat into that tube than it can take — and aluminium gives almost no colour warning before it collapses. The tube melts before the filler does, and a repair becomes a replacement.
So choose for the thin side and accept that a long fillet in heavy material will take a few more rods. Time is cheaper than a scrapped part.
What each diameter is for.
| Diameter | Typical joint | Notes |
|---|---|---|
| 1.6 mm | Thin-wall tube, small fittings, fine repairs | Least heat to get flowing. The safe choice on delicate work and small pinholes. |
| 2 mm | Light tube and sheet, general small repairs | The most popular size overall — enough fill rate without demanding much heat. |
| 2.2 mm | Medium sections | A half-step where 2 mm is slow and 2.5 is too much heat. |
| 2.5 mm | General fabrication | Good general-purpose workshop size for mixed medium work. |
| 3 mm | Heavier sections, longer fillets | Needs a torch with real output behind it. |
| 3.15 mm | Same duty as 3 mm | A standard metric wire step. Exists because some specifications call for it by name. |
| 4 mm | Thick sections, large fillets | Fastest fill rate, most heat required. Wrong choice on anything thin. |
On 3 against 3.15 mm: in practical use they behave the same. Unless your process document specifies 3.15 explicitly, either will do the job.
Mixed packs and repeat supply.
For a workshop taking varied jobs, a mixed pack is usually the sensible way to buy — cover thin tube and heavier sections without over-committing to a single diameter you may not need next week. Tell us the diameters and the split.
For a production or service operation running one size steadily, repeat supply against your usage pattern is straightforward to arrange. Either way, all diameters ship at 500 mm, which hand-feeds comfortably into a joint and packs without bending.
Common questions.
Which brazing rod diameter should I use?
Match the rod to the thickness of the thinnest part you are joining, not to the thickest. Thin-wall tube and small fittings want 1.6 to 2 mm, general fabrication and medium sections want 2.2 to 2.5 mm, and heavier sections or long fillets want 3 to 4 mm. Using too heavy a rod on thin material is the classic beginner error: the rod needs more heat than the part can survive, and you melt the tube instead of the filler.
What happens if the rod is too thin for the joint?
Nothing dangerous, just slow and inconsistent. You end up feeding rod after rod into the same fillet, and every restart is a place where the flux coverage and the fill can break down. Long joints in thick material are where a heavier rod genuinely pays for itself.
Why are there both 3 mm and 3.15 mm sizes?
They exist to match different specification conventions — 3.15 mm is a standard metric wire step, and some customers' process documents call for it explicitly. In practical use the two behave the same, so unless your paperwork specifies 3.15, either will do the job.
Can I order a mixed pack of diameters?
Yes, and for a workshop taking varied jobs it is usually the sensible way to buy — you cover thin tube and heavier sections without over-committing to one size. Tell us the diameters and the split you want and we will quote it.
Are all sizes 500 mm long?
Yes, every diameter is supplied at 500 mm. It is a practical length for hand feeding into a joint with a torch, and it packs and ships without bending.
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