Gas Fittings FAQs
Union nuts, tails, couplers, adaptors and clips for gas welding hose: how to choose them and fit them safely.
How do I work out which thread and size of fitting I need?
Start with the connection you are joining to, such as the regulator outlet or the blowpipe inlet, and read the thread size and hand (left or right) marked on it or given in the maker's data. Common gas welding connections use parallel threads in sizes such as 1/4 inch and 3/8 inch, with a left-hand thread for fuel gas and a right-hand thread for oxygen. The nut size is separate from the bore of the hose that goes on the tail.
Standards for hose connections set the dimensions of the union, nut and tail so that parts made to them fit together, but makers differ in detail. If you are unsure, check the existing part against the data plate or manual, or ask our team to help you identify it.
Do I need tape or paste on a hose union nut?
No. Gas welding hose unions generally seal on a face or washer, not on the thread. Parallel threads are made to hold the parts together, and the seal is made where two faces are pulled together with a seal between them. Tape or paste on the thread does not help the seal and can get into the gas path.
An equipment manufacturer's instructions also say not to use any jointing paste or tape between a regulator and the cylinder. Keep threads and seating faces clean and undamaged, and replace a washer or seat that is worn or marked, following the maker's instructions for your fitting.
How do I match a hose tail to my hose?
The tail has to suit the bore (inside diameter) of the hose, and the nut has to suit the thread of the connection it screws onto. These are two different sizes, which is why you will see tails sold as, for example, a particular bore for a particular nut size. Measure or check the marking on the hose, rather than guessing from the outside diameter.
The standard for hose connections covers the union, nut and other connection parts but not the design of the tail that goes inside the hose; hose assemblies are covered by a separate standard. A tail that is too loose or too tight in the hose can leak or damage the hose, so choose one made for gas welding hose of your bore.
Can I use ordinary worm-drive hose clips on gas welding hose?
No. HSE guidance says screw-tightened clips such as jubilee clips are not recommended for gas welding hose, because of the risk of leaks from over-tightening or under-tightening them. Hose tails should be refitted using crimp clips or ferrules designed for the task.
Use the type of clip or ferrule that the hose and fitting makers recommend, fitted with the correct tool, and follow your site rules. Replace a clip that has been removed rather than refitting it, unless the maker says it can be reused.