Maintenance & Troubleshooting MIG Consumables MIG Welding

How to Replace a MIG Liner: Steel vs PTFE, Measuring and Trimming, Step by Step

Steel or PTFE, how to measure and trim a MIG liner, and how to replace it step by step, with the signs that it is time for a new one.

Published November 4, 2026

Coiled steel MIG liner and PTFE MIG liner for aluminum wire, each with a brass end fitting

In this guide

Quick answer: To replace a MIG liner, turn the machine off, lay the gun cable out straight and remove the nozzle, contact tip and gas diffuser. Release the liner at the machine end, pull the old one out, feed the new one in and lock it. Then trim the front end to the length in your gun manual, so there is no gap and no bunching. Use a steel liner for steel, stainless and flux-cored wire, and a PTFE liner for aluminum.

Steel liner: Mild steel, stainless steel and flux-cored wire.
PTFE liner: Aluminum wire.
Size: Match your wire size, your gun model and your cable length.
Trim: No gap at the front and no bunching. Follow the gun manual or liner gauge.

Steel vs PTFE MIG liners: which one do you need?

A steel liner is a tightly wound steel coil. A PTFE liner is a smooth, slippery plastic tube. Choose by the wire you weld with.

Swipe sideways to see the whole drawing.

Inside the gun cable, the liner guides the wire all the way from the machine to the contact tip.

Feature	Steel liner	PTFE liner
What it is	A tightly wound steel coil	A smooth plastic tube
Use it for	Mild steel, stainless steel and flux-cored wire	Aluminum wire
Benefits	Tough and long-lasting with hard wire Handles the heat near the neck Stands up to cable bends better than plastic	Very low friction, so soft wire feeds smoothly Does not scrape or shave aluminum wire
Disadvantages	Scrapes and shaves soft aluminum wire More friction than plastic Can rust if stored damp	Kinks or crushes more easily Hard steel wire wears it faster Often needs a metal neck section to handle the heat near the tip

Which liner for your wire

Wire	Liner	Also match
Mild steel, solid	Steel	V-groove drive roll and a contact tip for the wire size
Stainless steel	Steel	V-groove drive roll and a contact tip for the wire size
Flux-cored	Steel	Knurled drive roll and a contact tip for the wire size
Aluminum	PTFE	U-groove drive roll, a contact tip made for aluminum, and a short cable or a spool gun

See the MIG wire size chart for matching parts to each wire size, and What size MIG gun do I need? for guns that feed aluminum well.

Signs your MIG liner needs replacing

The wire feed stutters or stops, even with the drive roll tension set right.
The wire birdnests at the drive rolls, or burns back to the tip with no change in settings.
Shavings, rust or dust come out of the end of the liner.
The wire is hard to pull through the gun by hand.
The liner or gun cable is kinked.
You changed to a wire size or type the liner is not made for.

See MIG birdnesting and burnback: causes and fixes to rule out the drive rolls and contact tip first.

How to measure a MIG liner

Wire size: liners are made for a range of wire sizes, such as .030 to .035 in. Choose one that covers the wire you use.
Gun model: the end fittings differ from gun to gun, so the liner must be made for your gun.
Cable length: buy the liner for your cable length, such as 10, 12, 15 or 25 ft. It comes slightly long so you can trim it to fit.
Trim length: use the length in your gun manual or a liner gauge. If the old liner fed well, you can lay the new one beside it and cut it to match.

How to replace a MIG liner, step by step

Most guns load the liner from the machine end, as below. Some load from the front, so check your gun manual first.

Turn the machine off, unplug the gun and let it cool.
Lay the gun cable out straight, with no loops or bends.
Remove the nozzle, contact tip and gas diffuser from the front of the gun.
Release the liner at the machine end by undoing the liner nut, collet or set screw.
Pull the old liner out in one smooth pull, keeping the cable straight. Keep it to compare lengths.
Blow out the empty cable with dry compressed air.
Feed the new liner in short pushes until it comes out at the neck, then lock it at the machine end without overtightening.
Trim the front end to the length in your gun manual or liner gauge, then file off any burr so the end is round and open.
Refit the gas diffuser, contact tip and nozzle, reconnect the gun, feed the wire through and run a test weld.

A PTFE liner for aluminum often comes with a short metal neck section and runs right up to the drive rolls at the machine end, as close as it can go without touching them. Follow the instructions that come with the liner. Shop necks and liners.

How to trim a MIG liner: too short vs too long

Swipe sideways to see the whole drawing.

The liner should end where the gas diffuser seats, with no gap and without being pushed back into the cable.

Trim	What happens
Too short	A gap is left at the front, so the wire can buckle there. Expect feed problems and birdnests.
Right	The diffuser screws on fully and the liner sits against it with no gap.
Too long	The liner bunches up inside the cable and the wire drags. The diffuser may not screw on fully.

Always trim with the cable laid straight. A liner cut while the cable is coiled ends up the wrong length once the cable is straightened.

How to make your liner last

Blow out the liner with dry compressed air each time you change the wire spool.
Use the right drive roll groove and tension, so the rolls do not shave the wire and fill the liner with dust.
Keep the gun cable straight while you weld, and coil it loosely when you put it away.
Do not run aluminum wire through a steel liner, or hard steel wire through a PTFE liner.

Safety when you change a liner

Turn the machine off and unplug the gun before you remove the liner.

Let the neck and nozzle cool before you touch them. Wear safety glasses when you blow out the cable with compressed air and when you cut the liner, because a steel liner springs and the cut end is sharp. Hold the loose end of the welding wire when you take it out, because it springs too. In Canada, CSA W117.2 covers safety in welding, cutting and allied processes. Always follow your gun and machine manuals.

Frequently asked questions

How do I know if my MIG liner is bad?

The wire stutters, stops or birdnests even with the drive rolls set right, or it is hard to pull through the gun by hand. Shavings, rust or dust coming out of the liner, or a kink in the cable, are also signs it needs replacing.

How often should a MIG liner be replaced?

There is no fixed schedule. Replace it when the wire starts to drag or the feed becomes unsteady. A quick check at each spool change is to pull the wire through the gun by hand: it should slide smoothly.

Can I use a steel liner for aluminum wire?

No. A steel liner scrapes and shaves soft aluminum wire, which causes drag and birdnests. Use a PTFE liner made for aluminum, with a U-groove drive roll and a contact tip made for aluminum.

Can I use a PTFE liner for steel wire?

It is not the usual choice. Hard steel wire wears a plastic liner faster, and a steel liner lasts longer with steel, stainless and flux-cored wire. Use a steel liner unless your gun manual says otherwise.

What size MIG liner do I need?

One that covers your wire size, fits your gun model and matches your cable length. Liners are made for a range of wire sizes, so check that your wire falls inside that range.

Where should I cut a MIG liner?

At the length your gun manual or liner gauge gives. On many guns, that is where the gas diffuser seats, so the diffuser screws on fully with no gap. Trim with the cable laid straight and remove any burr.

Do I need a new liner when I change wire size?

Only if the new wire falls outside the range the liner is made for, or you switch between steel and aluminum wire. You always need a contact tip that matches the new wire size.

Not sure which liner fits your gun?

Email a photo of your gun's machine-end connector and front end, with your cable length and wire size, to orders@mapindpro.com, call 905-919-1177, or visit our Toronto counter. We'll help you find the right liner.

Email us Call 905-919-1177 Shop liners

3625 Weston Road, Unit 10, Toronto, ON M9L 1V9. Monday to Thursday 8 am to 4:30 pm, Friday and Saturday 8 am to 12:30 pm.

TopicsMaintenance & Troubleshooting MIG Consumables MIG Welding