TIG Torch Adapter Fittings: 35 Dinse vs 5/8-18 Explained
By MIG/TIG/Stick Welders & Plasma Cutters | USA Weld – HTP ... | Published: 2026-10-13
Category: How-to Guides
Learn how to match a 35 Dinse TIG adapter, 5/8-18 LH water fitting, and torch series so your water-cooled or air-cooled setup connects correctly the first time.
Quick answer
A 35 Dinse adapter and a 5/8-18 fitting are two different connections on the same torch. The Dinse end plugs into your welder's power output, while the 5/8-18 end handles gas or water. For a water-cooled 20 series torch with a 7/8-14LH power cable fitting, use a 35 Dinse adapter with a 5/8-18 LH water fitting on the return line. Match both ends before you buy, because a correct power connection with the wrong water thread still will not seal.
What a 35 Dinse adapter actually connects
A 35 Dinse (1/2 in) adapter is the power-cable side of the connection. It lets a water-cooled 18 or 20 series TIG torch with the standard 7/8-14LH male power cable fitting plug into any welder that has a 35 Dinse (1/2 in) output. The adapter carries welding current; it does not carry gas or water by itself. If your welder has a flow-through gas connection, this style of adapter is intended for a torch with side gas only, so confirm how your machine routes shielding gas before ordering.
Why the 5/8-18 water fitting matters
The 5/8-18 thread is a common size for water return lines on TIG torches, and the LH (left-hand) direction tells you which way it tightens. A 35 Dinse adapter with a 5/8-18 LH water fitting gives you that return-line connection on the same body as the power plug. The hose color is not a specification; red or black hoses can both use the same thread, so match the fitting, not the color. If your torch uses a different thread or a right-hand fitting, this adapter will not seal correctly even if it threads on partway.
How to check your torch and welder before ordering
Write down three things: the torch series, the power-cable fitting on the torch, and the output socket on the welder. For example, a 20 series water-cooled torch with a 7/8-14LH male power fitting and a 35 Dinse welder output points to the 35 Dinse adapter with a 5/8-18 LH water fitting. For an air-cooled 9 series torch, the matching adapter is different: a 25 Dinse (3/8 in) adapter with flow-through gas is designed for 9 and 17 series torches. The two adapters are not interchangeable, so order by series and connection size, not by brand alone.
When to use a flow-through gas adapter instead
If your welder supplies shielding gas through the power connection rather than a separate hose, you need a flow-through gas adapter. A 25 Dinse (3/8 in) adapter with flow-through gas is built for 9 and 17 series TIG torches and provides a secure connection between the torch and power source while letting gas pass through. This is a different job from the 35 Dinse water-cooled adapter, which is for a torch with side gas only. Choosing the wrong one can leave you with no gas at the torch or a water line that will not connect.
Step-by-step: match and install your TIG torch adapter
- Identify your torch series and cable fitting: Find the series number on the torch body or handle and measure or read the power-cable fitting. A 20 series water-cooled torch commonly uses a 7/8-14LH male power fitting, while a 9 series air-cooled torch uses a 25 Dinse power connection. Checkpoint: if you cannot confirm the fitting size, do not order by guesswork.
- Identify your welder output socket: Look at the front or side of the welder where the torch power cable connects. A 35 Dinse (1/2 in) socket is larger than a 25 Dinse (3/8 in) socket, and the two do not interchange. Common mistake: assuming all Dinse connectors are the same size.
- Match the gas or water connection separately: The power side and the fluid side are separate. For a water-cooled 20 series torch, you need the 5/8-18 LH water fitting on the return line. For an air-cooled 9 series torch, you need a 5/8-18 RH gas fitting or a flow-through gas adapter. Checkpoint: left-hand and right-hand threads are not interchangeable.
- Choose the adapter that meets both ends: If you have a 35 Dinse welder and a water-cooled 18 or 20 series torch with a 7/8-14LH power fitting, the 35 Dinse adapter with 5/8-18 LH water fitting is the match. If you have a 9 or 17 series torch and a welder with flow-through gas, use the 25 Dinse flow-through gas adapter instead. Checkpoint: confirm side gas versus flow-through gas before you buy.
- Install and leak-check before welding: Thread the adapter onto the torch power cable and the water or gas line by hand first, then snug with the correct wrench. Turn on the cooler or gas flow and check for leaks or hissing at both connections before striking an arc. Common mistake: over-tightening a 5/8-18 fitting and damaging the threads.
Parts that match these connections
- 35 Dinse (1/2") Adapter with 5/8"-18 LH Water Fitting for 20 Series TIG Torches: 35 Dinse (1/2 in) adapter with a 5/8-18 LH water fitting for 20 series TIG torches; connects a water-cooled 18 or 20 series torch with a 7/8-14LH male power cable fitting to a welder with a 35 Dinse (1/2 in) connection. Use for a water-cooled torch with side gas only if the welder has a flow-through gas connection. This is the correct adapter when your torch has a 7/8-14LH power fitting and your welder has a 35 Dinse output, and you need a left-hand 5/8-18 water return connection.
- 9 Series (125A) Air-Cooled Torch w/25 Dinse & 5/8"-18 RH Gas Fitting: 9 Series (125A) air-cooled TIG torch with a 25 Dinse (3/8 in) power/current supply and a 5/8-18 RH gas fitting; one-piece flexible silicon rubber cable with nylon braided weave overlay that stays flexible in cold weather. If you run an air-cooled 9 series torch, this shows the matching 25 Dinse power side and a right-hand 5/8-18 gas fitting, which is not the same as the left-hand water fitting on the 35 Dinse adapter.
- 25 Dinse (3/8") Adapter with Flow Thru Gas for 9 and 17 Series TIG Torches: 25 Dinse (3/8 in) adapter with flow-through gas for 9 and 17 series TIG torches; provides a secure connection between torch and power source and a flow-through gas design for smooth gas flow. Use this when your welder routes shielding gas through the power connection and you run a 9 or 17 series torch, instead of a water-cooled 35 Dinse adapter.
