Spot welder: three different machines share the name. Which one you mean

Search for a spot welder and the results mix three unrelated machines. One squeezes two sheets of steel between copper tips. One joins nickel strip to battery cells. One is a gun that plugs into a stick welder. They do not overlap, so the first job is working out which one your project needs.

A spot welder usually means a resistance spot welder: tongs that clamp two overlapping sheets and pass welding current through them at one point. Home units handle thin mild steel only, rated by combined thickness, typically up to 1/8 or 3/16 inch. Battery tab welders and arc spot weld guns are different tools.

The three machines called a spot welder

Machine	How it joins	What it is for
Resistance spot welder	Tongs squeeze the sheets while current flows through the tips	Overlapping thin mild steel sheet
Battery tab welder	Short pulse of current through thin tabs	Nickel strip onto battery cells
Arc spot weld gun	An arc from a stick welder melts a top sheet into the one below	Sheet metal, from one side, using a welder you already own

The last one is Eastwood’s Spot Weld Gun. Eastwood’s own guide says it uses an electric arc, and to set the stick welder between 40 and 60 amps. If you own a stick welder, that is the cheapest route. Everything else on this page is about resistance welders.

Resistance spot welders a home shop can buy

Specs from each maker’s manual, checked 2026-09-27. Capacity is combined thickness of both sheets.

	Harbor Freight 61205	Harbor Freight 61206	Miller MSW-41T	Miller LMSW-52T
Input as published	120 V, 13.5 A	240 V, 16 A	110 V, 1.5 kVA	220 V, 2.5 kVA
Mild steel, combined	Up to 1/8 in	Up to 3/16 in	1/8 in	3/16 in
Galvanized	Two pieces of 20 gauge	Two pieces of 16 gauge	Remove coating first	Remove coating first
Duty cycle	50% over 10 s	50% over 10 s	50% over 10 s	50% over 10 s
Breaker or fuse	Not published	Not published	30 A, No. 10 wire	30 A, No. 10 wire
Tong length	Not published	Not published	6, 12 or 18 in	6, 12 or 18 in
Aluminum, copper	No	No	Not recommended	Not recommended

Sources: Harbor Freight manuals for 61205 and 61206; Miller owner’s manual OM-716, 2010 edition, archived copy.

We found no current Miller product page for either model, so treat them as possibly discontinued and a used-market find. Hobart’s spot welder category lists no products. Tecna makes hand-operated spot welders for body shops, but the model we checked is rated for 400 volt, 50 hertz European supply.

Longer tongs weld less

Miller publishes output current for each tong length, and it falls as the tongs get longer:

Tong length	MSW-41T output	LMSW-52T output
6 in	5,500 A	6,750 A
12 in	4,500 A	5,800 A
18 in	3,600 A	4,850 A

Tecna’s catalogue shows the same effect in thickness: its 7902 goes from 2.5 plus 2.5 mm on 125 mm arms to 1.2 plus 1.2 mm on 500 mm arms. Long tongs reach further into a panel and weld thinner stock. Buy the shortest tongs that reach your joint.

Duty cycle here is seconds, not minutes

On an arc welder, duty cycle is minutes of arc in every ten. On these resistance welders it is measured over ten seconds. Miller’s manual says 50 percent means the unit can weld for 5 seconds out of every 10. Miller’s timer sets the weld from 0 to 5 seconds; Harbor Freight’s unit welds while you hold the lever down.

Will your circuit run it?

The Harbor Freight 120 volt unit publishes 13.5 amps of input. Miller’s table gives a 30 amp fuse or breaker with No. 10 wire for both models. Harbor Freight publishes no breaker figure; its 240 volt manual asks for a grounded 240 volt receptacle with an appropriate in-line breaker. Both manuals ask for GFCI protection.

How those numbers meet your panel is in what size breaker a welder needs and can my panel handle a welder. OSHA’s resistance welding rule says equipment should be installed by a qualified electrician.

Safety from the manuals

• Pinch points. Miller says to keep hands from between the tips. OSHA requires finger clearance where the movable holder enters a portable gun frame.
• Pacemakers. Miller says wearers of pacemakers and other implanted medical devices should keep away. Harbor Freight says to consult a physician first.
• Sparks. Miller says to remove flammables within 35 feet of the weld.
• Eyes. Miller asks for safety glasses with side shields or a face shield. Harbor Freight asks for welding eye protection of at least shade 10; see the helmet shade chart.

Whether you need one at all

A resistance welder only joins overlapping sheets it can reach from both sides. Plenty of sheet metal work, including patch panels, is done with a mig welder instead. The welder for auto body guide compares how thin each mig welder is rated to go, and welding machines walks through choosing a first machine.