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.
What is the difference between a hose coupler and a hose splicer?
A coupler has a thread or connection at each end, such as two union nuts, and is used to join two threaded hose ends or to join a hose to a threaded component. A splicer is a straight tail-to-tail joiner that goes inside two hose ends. Choose the one that matches the ends you are joining.
Both add a joint, and every joint is a possible leak point and a point where the hose can be strained. Where possible, use a single length of hose of the right size rather than several short lengths joined together, and use only parts that are made for gas welding hose and suit the gas and the bore.