Brazing nozzle sizes explained

The number on a brazing nozzle is a code for orifice diameter and gas flow - not a physical length. A bigger number means a wider orifice and more heat at the joint. Because the number is standard across the British No. series, you can order a replacement without measuring anything: match the stamp, confirm the seat, done.

British-style brazing nozzles run up the No. series from light work to heavy. As a working guide: No. 8 for light silver brazing and small-bore tube, No. 10 for small fittings and general light brazing, No. 13 for general copper/brass/steel brazing up to medium section, No. 16 for heavier joints and light pre-heat, and No. 20-25 for heavy section and substantial pre-heat.

Note that the brazing series is separate from the acetylene welding No. 1-25 series - the two are sized and shaped differently.

The rule of thumb: fit the smallest nozzle that flows the joint in good time - it gives the cleanest result and wastes the least gas. For a 15-22 mm copper or brass joint, No. 10 is the everyday answer; drop to No. 8 for delicate work and step up when the joint is slow to flow.

The size you need is set by the mass of metal at the joint, not by the tube diameter printed on the fitting. A thick cast boss and a thin drawn tube of the same diameter want very different flames: the boss soaks heat up, the tube lets it run away.

Look at the joint the way the flame has to. How much metal is there, and how fast does it pull heat away? A small, thin, tight-fitting joint comes up to temperature on a small flame. A chunky section - a boss, a flange, a heavy bracket - needs a wider flame to bring the whole mass up together, otherwise the surface scorches while the middle stays cold.

Start from that section, then move one step in the direction of the job. Delicate, thin-walled work wants the smaller side; heavy, chunky work wants the larger. The number is shorthand for that decision, not a length to measure.

A nozzle that is too large does three things, none of them good. It burns more gas than the joint needs, which you feel across a day of bench work. It widens the heat-affected zone, so the metal around the joint softens and discolours far beyond where the filler is going. And on thin sections it simply burns through - the metal lets go before you have finished moving the flame.

A too-small nozzle fails more gently: the joint is slow, the filler sits on the surface instead of flowing, and you are tempted to force it with more heat until the flux burns. Both mistakes end the same way - a joint that looks done but is not. Read the metal, not the clock, and let the soldering vs brazing guide settle which process you are even doing.

A brazing nozzle throws a softer, wider flame envelope so the filler flows into the joint without melting the base metal. A welding nozzle concentrates heat for fusion welding. Different gas set-ups also matter: oxy-acetylene and oxy-propane use different size equivalents, so always read the product table for your gas. The welding nozzle collection lists the No. 1-25 series by gas.

A single-flame brazing nozzle covers most repair and production work, but two other shapes appear where the job is awkward. A multi-flame nozzle spreads several small cones over a wide area, which suits heating a long seam or a large flat face evenly. A rosebud throws a bushy, soft flame for pre-heating heavy sections before the brazing flame goes on.

Neither replaces the everyday brazing nozzle. They are specialists for heating, and they sit in the same brazing nozzle collection so you can match the seat and the series in one place. If your work is mostly joints, start with the single flame and add the heating shapes only when a job keeps asking for them.

The number is a sizing code, not a fitting standard. Two nozzles stamped with the same number can still have different seats, and a nozzle that threads onto one torch head may not seal on another. The seat is where the gas seals - get it wrong and the joint leaks at the torch, not at the work.

Before you order, confirm the seat against your torch head on the compatibility chart. If the chart does not settle it, send us the torch model and a photo of the old nozzle and we will match it. A number without a seat match is a guess, and a guess at a gas connection is not a small risk.

Read the stamp on your old nozzle, then check the seat and thread against your torch head. For the bench, the 3-size set covers most work; if you know your staple size, buy the single - No. 10 is the most re-ordered brazing size for a reason. Not sure? Send us your torch model and we will match it.

You can test a size in minutes before you commit to a real job. Set the flame neutral, bring it onto a scrap of the same section as your work, and watch the filler. If the filler wets and flows into the joint in a steady, controllable pass, the size is right.

If the filler balls up and sits on the surface, go up a size. If the metal around the joint sags, colours heavily or starts to sink, come down a size. A few minutes on scrap settles what no chart can, and the brazing rods you use for the test are the same ones you will use on the job.

Clean carbon off regularly with a tip cleaner set, and replace a nozzle when the orifice is oval or the flame splits - a worn brazing nozzle wastes gas and makes joints slowly, no matter how well it is cleaned.