This category covers welding hose, twin hose, pigtails, fittings, adapters, valves and repair parts.
Hose grade follows the gas. Grade R is for acetylene only and must never be used with propane or propylene, which degrade the tube from the inside and eventually cause a leak at a fitting. Grade T handles all fuel gases including propane, propylene, MAPP and natural gas. Grade RM is for oxygen. Twin hose assemblies pair an oxygen line and a fuel line with different thread fittings so the two cannot be cross-connected.
Fittings are specified by thread type and size. NPT is the standard tapered pipe thread; SAE and JIC flare fittings appear on hydraulic and some gas connections; B-size and A-size refer to the CGA fitting series used on torches and regulators. Left-hand thread is used on fuel gas connections throughout, which is why fuel fittings will not thread onto oxygen outlets.
Hose repair kits, ferrules and crimp fittings let a damaged hose be repaired rather than replaced. The repair must use the correct ferrule for the hose grade and be crimped properly — a clamp-on repair on a high-pressure line is not acceptable.
Flashback arrestors and check valves prevent a flame from travelling back up the hose into the regulator and cylinder. They are required on oxy-fuel setups in most jurisdictions and should be fitted at both the regulator and the torch end. Check valves alone stop reverse flow but not a flame; arrestors are what stop the flame.
