Torch nozzle seats: why the same size number does not always fit

A nozzle has two jobs and two corresponding surfaces. The bore shapes the flame, and the seat mates with the torch body or head. The bore gets all the attention, because it is what you can see working. The seat does the work you cannot see, hidden inside the joint between nozzle and body.

The seat is the machined face - or cone, or shoulder - where the nozzle meets the body and seals against gas. If that surface does not match the body it is screwed into, the nozzle will not seal, whatever number is stamped on the side of it. Gas takes the path of least resistance, and it has no interest in what the catalogue said.

This is why two nozzles of identical output can be completely interchangeable in flame terms and completely incompatible in practice. Output is about the bore. Fitment is about the seat. It is also why buying on a flame description alone tends to end in a return.

Nozzle numbers are series numbers, not universal sizes. A "No.5" is the fifth step in one maker’s series, sized against that maker’s burners. Another maker’s No.5 is the fifth step in a different series, on a different body, with a different seat.

So two nozzles can carry the same number, produce a broadly similar flame, and still be unusable on each other’s torches. The number tells you about output within a family. It tells you nothing about fitment between families. Within one maker’s own series the numbering is perfectly consistent and genuinely useful - it simply does not travel.

The same trap appears in shorthand like "medium" or "large", which is why we would rather you sent a photograph than a size. A photo of the seat settles it; a size word rarely does. Two minutes with a camera beats twenty minutes with a comparison table.

Seats are grouped by the shape of the mating surface. The families you meet in practice include flat-faced seats that seal against a machined face, tapered or conical seats that wedge into a matching cone, shouldered seats that locate on a step, and threaded patterns that differ in how the nozzle is retained.

We describe these by concept on purpose. The useful fact is which family your torch belongs to - not a dimension, and not a figure you can sensibly compare across brands. Angles and diameters vary between makers even inside the same broad family. A seat can look right to the eye and still not seal, which is why fitment is confirmed by assembly rather than by appearance.

Our compatibility chart groups what we sell into five seat families for exactly that reason: it lets you shop by mating geometry instead of by a number that means nothing outside its own series. Once you know which family your torch sits in, the rest of the range opens up without any further guessing.

Rothenberger, Sievert and Bullfinch each developed their own bodies and their own series. That means a cross-brand equivalence is an inference, not a fact, until somebody has actually screwed the two parts together and checked the seal. Even within a single brand, a nozzle that fits an older body will not always fit the current one.

Our parts are third-party spares. Brand names appear on this site purely as a fitment reference - we are not affiliated with, authorised by, or connected to any of those brands, and we do not claim that any part of ours is genuine for them. A fitment reference is not an approval, and it is worth reading listings with that distinction in mind.

So if you need a Rothenberger Superfire 2 spare, a Sievert spare or a Bullfinch spare, send the model and a photo and we will check it against the seat rather than against a name on a chart. If a seller tells you a part fits without asking which model you have, ask again.

A nozzle that nearly fits is worse than one that obviously does not. It threads part-way, feels tight enough, and then leaks gas at the seat - which you may notice as a hiss, a smell, or simply a flame that refuses to behave the way it should.

A leaking seat can let the flame light back inside the mixing chamber. At best you get a popping, unstable flame; at worst you get a flashback and a ruined head. A nozzle sitting off-axis also throws the flame crooked, which reads as a yellow or lazy flame while the real fault is mechanical. Both of those symptoms get blamed on the gas, and neither of them is the gas’s fault.

And if you force a wrong-fit nozzle to tighten, you gall the seat on the body. That damage is on the torch, not on the cheap part - so the mistake outlives the nozzle that caused it. If a nozzle will not run on by hand, stop there: that is the answer.

Photographs settle it. Send the nozzle side-on with any stamped number readable, a straight-on shot of the seat face, and the torch body or head showing its model marking. A photo of the two parts together, unscrewed, helps as well.

Add the model name off the torch, and the job if it matters - soldering, brazing and welding nozzles are different nozzle series with different seats, so "the nozzle for my torch" is rarely a complete answer. A photo of the old nozzle beside a rule helps if there is no model marking left to read.

We reply with a match, a non-match, or a request for one more angle. Start on the contact page; it costs one message and removes the guesswork entirely.

It groups what we sell by seat family, so you can find parts that share a mating geometry rather than a marketing number. That removes most of the guesswork once you know which family your torch sits in.

What it cannot do is tell you your torch’s family from a brand name alone. Bodies change across production runs, and the same brand has used more than one seat over the years. Older kit is the usual case, since bodies were revised more often than the catalogues ever suggested. Use the chart to narrow the field, then confirm with a photo.

Treat it as a filter with a human check at the end, not as a lookup table. That is the honest way to buy spares across brands that never agreed a common seat in the first place.

Order one nozzle first and test the fit before buying a set. Check that it seats by hand and seals before you light it - a hiss at the joint is the sound you are listening for, or rather, hoping not to hear. Do the trial fit before you need it, not on the job, so a wrong part costs you an evening rather than a day.

Keep seat faces clean and undamaged in storage, and retire any nozzle that has been forced on. Once a seat face is scored, it will not seal properly again, and the fault will follow you to the next torch body. Store nozzles so the faces cannot knock against each other in a bag.

The consumable side is easier: the seals in our service kit cover the wearable parts of the head, and a tip cleaner keeps the bore clear once the fit is right.