Oxy-acetylene welding nozzle numbers: No. 1–25 explained
FLAMESPARES LEARN — PRACTICAL SIZING & SETUP GUIDES
The No. 1–25 system
UK and European oxy-acetylene welding nozzles are numbered by gas-flow capacity, from No. 1 (smallest) to No. 25 (largest). The number is stamped on the nozzle body and printed on every product page — match the stamp, not the memory.
Number → flow → metal thickness
The number tracks the orifice and the acetylene flow, and the flow tracks the metal you can weld. The launch range covers No. 1–10 for welding duty, with the high numbers (No. 16 and up) reserved for heavy heating and pre-heat work. Acetylene values are shown on the tables; propane equivalents differ ⚠.
Which size welds what
Thin sheet and fine work: No. 1–3. General plate: No. 4–6 — with No. 5 the workshop default. Heavy plate: No. 7–10. From No. 16 up, you are in heating and pre-heat territory, not welding. Read the flame as you work: a too-small nozzle drowns the puddle; a too-large one blasts it apart.
Sets vs single numbers
A set covers a shop full of jobs — the No. 1–10 set is the one most workshops buy first. When you know your staple thickness, buy the single: No. 5 is the UK reorder king for general plate, and No. 16 is the heating and pre-heat specialist.
Verifying fit before you buy
The No. series is a sizing code, not a universal thread. Your torch head must accept the British No. series seat ⚠. Check the compatibility chart, or send us your torch model and we will confirm the fit before you order.
Using numbers safely
Set regulator pressures from the nozzle rating ⚠, light with a flint rather than a lighter, and never run acetylene above its working pressure. Keep nozzles clean with a tip cleaner set and store the set in its case.
Quick answers
What does No. 5 mean on an acetylene welding nozzle?
It is the British capacity code for a medium welding size (⚠ orifice ~0.56 mm, flow ~55–85 g/h acetylene) — the default for general plate work.
Is No. 16 a welding nozzle?
No. 16 sits at the heating end of the series: it pre-heats thick stock and castings. Weld with the lower numbers, heat with the higher ones.
Do these numbers match the torch brand I own?
The No. series is a sizing code used across British-style heads; the physical seat still has to match your torch — verify on the compatibility chart or send us the model.