What's inside
As an Amazon Associate I earn from qualifying purchases. This post may contain affiliate links at no extra cost to you.
On a TIG welder, 2T and 4T are trigger-control modes. They do not change the welding process, shielding gas, tungsten type, or arc characteristics by themselves. They change how the torch switch starts and stops the arc.
For short welds, the difference is minor. For long welds, it affects hand fatigue, torch control, heat management, and the chance of accidentally stopping the weld. The cheaper or simpler 2T mode is perfectly adequate for many jobs, but 4T is usually more comfortable when a weld takes several minutes or requires both hands to stay steady.
What 2T mode does
In 2T mode, the torch trigger must be held for the entire weld. Pressing the trigger starts the programmed sequence, and releasing it stops the arc. The “two touches” are the trigger press and trigger release.
Depending on the machine, pressing the switch may begin pre-flow, ignition, and upslope before reaching the set welding current. Releasing it may activate downslope, crater current, post-flow, and final arc shutoff. The exact sequence depends on the welder’s controls.
2T is straightforward and predictable. It is useful for tacks, short fillet welds, small repairs, and work where you need to stop immediately when the joint changes. It also works well with a foot pedal if the welder supports pedal control, although pedal operation may override or work differently from the torch-trigger settings.
The main weakness is hand fatigue. Holding a torch button for a 24-inch aluminum seam can make your grip tighten, which makes torch height and travel speed less consistent. A tired hand is more likely to lift the tungsten, drag the cup, or move off the joint.
What 4T mode does
4T mode is a latching trigger sequence. A common operation is:
-
Press and hold the trigger to start the arc.
-
Release the trigger to keep welding without holding the button.
-
Press and hold the trigger again when you want to stop.
-
Release the trigger to run downslope, crater fill, and post-flow.
Some welders use slightly different timing, such as entering a lower starting current during the first press or a crater current during the second press. Read the machine manual before relying on 4T for a critical weld. On many machines, a quick press-and-release starts the weld, while a second press-and-release ends it; on others, the trigger must be held during part of the sequence.
The useful feature is that your trigger hand can relax after the arc starts. You can concentrate on torch angle, filler-rod timing, and travel speed instead of squeezing a small switch. This is especially helpful when wearing thick welding gloves.
2T vs 4T for long TIG welds
| Factor | 2T | 4T |
|---|---|---|
| Trigger operation | Hold for the full weld | Latch on and off through a sequence |
| Best use | Short welds, tacks, repairs | Long seams and repeated production welds |
| Hand fatigue | Higher | Lower |
| Stopping control | Immediate and simple | Requires learning the sequence |
| Risk for beginners | Accidental release stops the arc | Incorrect switch timing can start or end the sequence unexpectedly |
| Equipment requirement | Available on most TIG welders | Must be supported by the welder and torch control |
For a long stainless or mild-steel seam, 4T can improve consistency because your hand is less tense. That does not automatically make the weld better. Poor joint fit-up, excessive amperage, inadequate shielding, or a dirty tungsten will still cause defects. 4T only removes one source of operator fatigue.
Downslope and crater-fill settings matter more
Trigger mode is only part of the stopping sequence. A TIG welder with adjustable downslope lets current taper down instead of shutting off abruptly. This reduces the crater and helps prevent a crack at the end of the weld, particularly in aluminum and alloys that are sensitive to crater cracking.
For many manual welds, a downslope of roughly 2 to 5 seconds is a useful starting range. Thin sheet may need less, while a thick, hot joint may need more. If the puddle suddenly shrinks or the tungsten extinguishes before the crater is filled, the setting may be too short. If the end remains overheated or the weld becomes excessively wide, it may be too long.
Set post-flow long enough to protect the hot tungsten from oxidation. A common starting point is about 1 second per 10 amps, though material thickness, cup size, and gas coverage change the requirement. At 150 amps, roughly 10 to 15 seconds is often reasonable. A purple, blue, or gray tungsten after the weld is a warning that shielding or post-flow is inadequate.
When 2T is the better choice
Buy or use 2T without concern if most of your work involves welds under 6 inches, frequent stops, tack welding, or awkward joints where you need instant control. A basic machine with 2T, adjustable pre-flow and post-flow, and usable downslope can produce excellent welds.
2T is also preferable when several people use the welder and nobody wants to remember a special latch sequence. It is easier to troubleshoot: hold the trigger to weld, release it to stop. If you are learning TIG, 2T lets you focus on arc length and puddle control before adding trigger timing to the job.
When 4T is worth paying for
Choose 4T when you regularly weld long seams, work with a heavy torch, wear bulky gloves, or need to keep both hands stable for filler addition. It is particularly useful for fabrication tables, exhaust components, tanks, frames, and stainless tubing where a continuous bead may last 30 seconds or longer.
Before buying, confirm that the machine actually includes 4T rather than assuming every TIG welder does. Check the torch connector and control arrangement as well. Some welders need a compatible torch switch, while others require a separate remote control. A convenient starting point is to compare AC/DC TIG welders with 4T trigger mode.
If you weld aluminum, also prioritize adjustable AC frequency, AC balance, downslope, and sufficient duty cycle. A 4T function does not compensate for a machine that overheats halfway through a long weld. For a 200-amp machine rated at 40 percent duty cycle, expect approximately 4 minutes of welding in a 10-minute period at its rated output.
A practical setup for a long weld
Fit up and clean the joint first. Set amperage according to material thickness, then use 2T while practicing the start and stop sequence. Once the weld parameters are stable, switch to 4T and rehearse the trigger movements without an arc.
Position the torch cable so it does not pull on your wrist. Start with the cup close to the joint, establish a consistent arc length, and begin downslope while the puddle still has enough heat to accept filler. Do not lift the torch immediately at arc shutoff; hold position through post-flow so the hot tungsten and weld end remain shielded.
For most home shops, 2T is the sensible minimum and 4T is a comfort and consistency upgrade. If long welds are routine, the upgrade is worthwhile. If they are occasional, spend the money first on a stable TIG torch with a comfortable switch, proper gas control, and a machine with adjustable downslope.