← All guides

Lampworking Torch Fittings, Hoses, and Connectors: How to Plumb a Glass Torch Safely

Lampworking torch fittings explained: B fittings and left-hand fuel threads, Grade R vs Grade T hose, Y connectors for oxygen, single- vs multi-stage hookup, plus a parts checklist.

cluster · published

By Joe Blanchard · Updated

Lampworking Torch Fittings, Hoses, and Connectors: How to Plumb a Glass Torch Safely

Short answer: A glass torch connects to two supplies — a fuel gas (propane or natural gas) and oxygen — and each supply gets its own regulator, its own flashback arrestor mounted right at the regulator (before the hose), and its own hose running to one of the torch’s two inlets. The hose-to-torch connections are almost always “B” size (9/16”-18 thread), where the fuel side uses a left-hand (reverse) thread with a notched nut and the oxygen side uses a right-hand thread — a deliberate safety standard so the two gases physically cannot be cross-connected. For a propane or natural-gas lampworking setup you want Grade T welding hose (rated for all fuel gases), not Grade R. If you need to split or combine oxygen — joining two concentrators, or feeding a multi-port torch — that’s a Y connector job, with cautions. Below is how every piece fits together, plus a parts checklist.

This article assumes you’ve already chosen a torch and an oxygen supply. If you haven’t, start with the complete glass torch buyer’s guide and the oxygen concentrator vs tanks breakdown — and read the glass torch safety setup checklist alongside this one, because plumbing and safety are the same job.

Not a substitute for professional guidance. Fitting sizes, hose grades, and hookups below reflect widely published welding-gas and lampworking conventions, but your torch maker’s instructions and your gas supplier’s guidance always win. Confirm every fitting, thread, and hose with the maker or supplier before you connect anything, and have a qualified professional check an unfamiliar setup.

The full path: supply → regulator → flashback arrestor → hose → torch

Every flameworking torch is fed by two independent lines that meet only inside the torch head, where fuel and oxygen finally mix. From each supply, the order is the same:

  1. Supply — a fuel source (propane cylinder, or natural gas plumbed to the space) and an oxygen source (compressed cylinder, or an oxygen concentrator).
  2. Regulator — each gas gets its own dedicated regulator for that gas and pressure range; they are not interchangeable. (A concentrator is low-pressure and plumbed differently from a regulated cylinder — see the oxygen supply guide.)
  3. Flashback arrestor — a small inline device on both lines that stops a flame or reverse gas flow from traveling back toward the regulator and supply. It mounts right at the regulator outlet, before the hose (one on the fuel regulator, one on the oxygen regulator), so the hose itself is protected too. (A torch-end check valve may also be fitted, but the flashback arrestors themselves go at the regulator.)
  4. Hose — the correct welding hose for each gas; fuel and oxygen hose are distinct and usually color-coded (red/fuel, green/oxygen).
  5. Torch inlets — the two lines connect to the torch’s two inlets, each via the correct fitting.

The rule running through all of it: fuel hardware and oxygen hardware are deliberately different so they can’t be swapped — keep them that way. Flashback arrestors belong on both lines, not just the fuel side (covered in depth in the safety setup guide).

B fittings: the standard oxy-fuel connection (and why fuel threads run backwards)

When people say a torch uses a “B fitting,” they mean the B-size welding hose connection, which uses a 9/16”-18 UNF thread. B size is the most common oxy-fuel hose connection on medium-duty torches and is what most lampworking torches and regulators use. (Welding hose connections come in A, B, C, and D sizes; B is the everyday middle size.) Source: Harris Products Group.

Here’s the safety-critical part. On a B (and A and C) connection:

  • The oxygen side uses a right-hand thread — it tightens the normal way, clockwise. In CGA fitting terms this is CGA-022.
  • The fuel-gas side uses a left-hand (reverse) thread — it tightens counter-clockwise. In CGA terms this is CGA-023.

Source: CONCOA CGA fitting reference, Rexarc.

The notch is the “this is the fuel thread” signal — and why it exists

Because a left-hand thread isn’t obvious by eye, fuel-gas fittings carry a distinctive notch (a groove machined around the circumference of the nut or hex) — the universal visual indicator of a left-hand thread. See a notch, expect a reverse thread, and you’re on the fuel side; oxygen nuts are smooth. The reverse thread is a mechanical safeguard: the fuel nut won’t thread onto an oxygen port (or vice versa), so you physically cannot cross-connect fuel to an oxygen regulator or oxygen to a fuel outlet. Since the whole hazard of oxy-fuel work is keeping the two gases apart until the torch mixes them deliberately, never “adapt” or force a fitting to make a wrong connection work. Source: Rexarc, Chaotic Glass (Mike Aurelius), “Decoding the welding fittings”.

Practical note for lampworkers: an oxygen concentrator usually outputs through a small hose-barb, not a B fitting, so concentrator setups often use a female “B” oxygen nut → 1/4” hose-barb adapter to bridge the concentrator tubing to B-fitting hardware. Confirm the exact adapter with your maker. Source: Lampwork Etc., “Connecting two oxygen concentrators”.

Welding hose grades: use Grade T, not Grade R, for propane or natural gas

Welding hose is classified by grade under the RMA/CGA IP-7 standard, and the grade tells you which fuel gases the hose is safe to carry. This matters for lampworking because most lampworkers run propane or natural gas, not acetylene — and the wrong grade degrades.

  • Grade R — acetylene only. Tube and cover are not oil-resistant and not flame-resistant. Because Grade R isn’t oil-resistant, the oils in propane / LP gas will attack it over time (it can soften, get tacky, and crack), so Grade R is not advised for propane, LP, propylene, or natural gas.
  • Grade RM — has a flame- and oil-resistant cover but a tube that is not oil/flame-resistant. Some vendors market RM as “multi-fuel,” but the grade’s tube limitation makes it ambiguous; for a non-acetylene fuel the unambiguous correct choice is Grade T. If you see Grade RM offered, confirm its fuel rating with the supplier rather than assuming.
  • Grade T — all fuel gases, including acetylene, propane, propylene, MAPP, and natural gas. Tube and cover are flame- and oil-resistant. If you use any fuel gas other than acetylene, you should use Grade T to guarantee compatibility.

Source: Gas Innovations, “Welding Hose Safety Bulletin #5”, CrossCo, “Selecting a Welding Hose” (TB4802).

Bottom line: for a propane / natural-gas + oxygen lampworking setup, use twin Grade T hose — it’s rated for your fuel and oxygen and tolerates the oils in LP gas. This corrects a common myth: Grade R is the acetylene hose, not the “LP-only” hose — it’s the wrong one for propane. Color-coding (green oxygen, red fuel) is a convenience, not a substitute for the grade stamped on the hose. Source: Gas Innovations.

Y connectors, splitters, and manifolds: splitting or combining oxygen

A Y connector (or splitter / manifold) joins or divides a gas line. In lampworking it shows up in two common situations, both on the oxygen side:

Combining two oxygen concentrators into one supply

A single concentrator often can’t feed a hungry torch, so lampworkers plumb two (or more) concentrators together with a Y connector to add their flows. The standard build uses a female “B” oxygen nut to 1/4” hose-barb fitting on each concentrator, joined into a Y splitter that combines the outputs; many of these Ys include silicone flap check valves so one unit can’t backflow into the other. Source: Lampwork Etc., “Connecting two oxygen concentrators”.

The crucial caution — repeated from the oxygen supply guide because people get burned by it — is that combining concentrators adds volume (flow / LPM), not pressure. Concentrators are low-pressure (a few PSI); two 5-PSI machines still give ~5 PSI, just more usable oxygen at that pressure. Forcing more than the maker intends can hurt purity and damage the sieve beds. Source: Lampwork Etc..

Feeding a multi-port torch

Multi-stage torches (next section) have separate fires with separate inlets, so a manifold or Y can feed those ports — and can mix oxygen sources (concentrator on one fire, tank on another).

Cautions for any Y / splitter: use oxygen-rated hardware for oxygen and never Y a fuel line to an oxygen line; install any check valves in the correct direction; soapy-water leak-check every added joint before lighting; and remember a Y is plumbing, not a flashback arrestor — you still need an arrestor on each line.

Single-stage vs multi-stage hookup

How many lines a torch needs depends on its stage count — the number of independently valved “fires” it has.

Single-stage torches: one fuel + one oxygen line

A single-stage torch (most beginner and many intermediate bench torches) has one fuel inlet and one oxygen inlet. The hookup is exactly the path described above: one regulated fuel line and one regulated oxygen line, each with a flashback arrestor, into the two inlets. Simple, and a single oxygen concentrator or one cylinder commonly feeds it.

Multi-stage torches: more fires, more oxygen, sometimes more lines

Multi-stage torches (2-stage and 3-stage are common) have independently controlled center, middle, and/or outer fires — for example GTT’s 2-stage Mirage or the 3-stage Kobuki and Samurai, each with separately valved center/middle/outer fires. Source: Mountain Glass, “GTT Torches”.

Two consequences for plumbing:

  • They want more oxygen. Opening additional fires raises oxygen demand well beyond a small single-stage torch, so big multi-stage torches often need tanked oxygen, bulk oxygen, or multiple concentrators rather than one unit. (A large torch like the Sidewinder is described as running on two or three concentrators for full performance.) Source: Mountain Glass, “Best Torches for Lampworking or Glassblowing”.
  • They can take separate or mixed oxygen lines. Because the fires are independent, you can route different oxygen sources to different fires — a common real-world trick is a concentrator on the thrifty center fire and tanked oxygen on the thirsty outer fire, with the fuel “Y”ed together at the torch. A multi-stud manifold (e.g., a 4-stud Mirage) is built for this. Source: Lampwork Etc., “Oxygen concentrator + tanked O2”, Mountain Glass.

For completeness: 4-stage torches are rare — essentially the only one is GTT’s Quadzilla, a custom-built-to-order “4-stage super torch” that is not a stock item. If you’re plumbing one of those, you’re well past beginner territory and should work directly from GTT’s instructions. Source: GTT Site Master, “Quadzilla”.

Connection and parts checklist

The list below is a qualitative checklist, not a specification for your exact torch — sizes, grades, and hardware vary by model and supplier, and the items are unverified for your specific setup. Confirm each one with your torch maker and gas supplier before buying or connecting.

PartFuel sideOxygen sideNotes
RegulatorFuel-gas regulator for your fuelOxygen regulator (cleaned for oxygen)Dedicated per gas; never interchange
HoseTwin Grade T welding hose (propane/NG)Twin Grade T (or oxygen line of the twin set)Grade T = all fuel gases; avoid Grade R for propane
Hose-to-torch fittingB size, left-hand thread, notched nutB size, right-hand thread, smooth nut9/16”-18; CGA-023 fuel / CGA-022 oxygen
Flashback arrestorOne at the fuel regulatorOne at the oxygen regulatorMount at the regulator, before the hose; both lines — not optional
Concentrator adapter—Female “B” oxygen → 1/4” hose-barbBridges concentrator tubing to B hardware
Y / splitter (if used)(rare on fuel)Y to combine concentrators or feed multi-portAdds flow, not pressure; check-valve direction matters
Leak checkSoapy water on every jointSoapy water on every jointNever check with a flame

Key takeaways

  • A torch is fed by two independent lines (fuel and oxygen), each with its own regulator, flashback arrestor, and hose — the arrestor mounts at the regulator, before the hose, on both lines.
  • B fittings are the standard oxy-fuel connection (9/16”-18): fuel = left-hand thread, notched nut (CGA-023); oxygen = right-hand thread, smooth nut (CGA-022). The reverse thread keeps fuel and oxygen from being cross-connected — never force a fitting.
  • For propane or natural gas, use Grade T hose (all fuel gases, oil- and flame-resistant). Grade R is acetylene-only and degrades on propane — not the “propane hose.” Treat Grade RM as ambiguous and confirm its rating.
  • Y connectors combine concentrators (adding flow, not pressure) or feed multi-port torches — but a Y is plumbing, not a flashback arrestor.
  • Single-stage torches need one fuel + one oxygen line; multi-stage torches want more oxygen and may use separate or mixed oxygen lines. 4-stage torches are rare (GTT Quadzilla, built to order).
  • Everything here is qualitative and unverified for your setup — confirm with the maker and supplier. This is not a substitute for the manufacturer’s instructions or a qualified professional.

Sources

Editor’s note: fitting sizes, hose grades, and CGA conventions reflect published welding-gas and lampworking sources as of 2026. Hardware and configurations vary by torch and supplier — always confirm the exact fittings, hose grade, and hookup with your torch manufacturer and gas supplier, and consult a qualified professional for an unfamiliar setup.

Sources