Welding workholding and fixturing: welding magnets (90°/multi-angle squares), magnetic ground clamps, locking and C-clamps, and fixture-table clamp sets for the home and small fab shop

magnetic welding ground clamp  · 

Welding magnets: fixed-angle squares, multi-angle and switchable types

A welding magnet is a ferrous holder that sets two pieces at a known angle so you can tack them without a third hand. Most are arrow- or triangle-shaped. The fixed 90° square is the workhorse for T-joints and box corners. The multi-angle version adds 45° and 135° faces, and sometimes 30°, 60° and 75°, which covers mitered frames, gussets and trailer or gate corners.

Switchable magnets have a lever or knob that turns the magnetic circuit on and off, so you can release a part without prying. They cost more than fixed ferrite squares. They also give a firmer hold on thicker plate, and they let you reposition a part without fighting the pull. Fixed squares are simpler and have nothing to jam with spatter, but you have to knock or lever them off after tacking.

Buy by the angles your projects need, not by the biggest angle count on the box. A set of 90° squares plus one multi-angle unit suits most home fabrication. Two or three squares let you hold both sides of a corner at once.

Pull force, heat and the limits of magnetic holding

Pull force is usually rated in pounds on clean, flat, mild steel. That number is a maximum, not what you get on rusty, painted, curved or thin stock. A magnet on thin sheet saturates it and loses grip. A magnet on mill scale or paint holds noticeably less because the air gap weakens the circuit. Look for ground, flat working faces and read the rated pull as a ceiling.

Magnets work only on ferromagnetic metal. They will not hold aluminum or austenitic stainless such as 304 and 316, which are essentially non-magnetic. Those jobs need clamps.

Heat is the other constraint. Neodymium magnets can lose strength permanently if they get hot, and the loss starts well below the temperature of freshly welded plate. Ferrite types tolerate more heat but hold less per unit size. Keep magnets back from the joint, and don’t leave one against a part you’ve just welded.

Magnetic fields can also cause arc blow, where the arc wanders or pushes to one side. If you see it near a magnet, move or remove the magnet, or re-position your ground. Don’t use a magnet as a permanent fixture for the whole weld sequence: tack, check square, then remove it before the final passes.

Magnetic ground clamp vs spring clamp

The work clamp carries the full welding current back to the machine, so its contact quality affects arc stability. A spring-loaded ground clamp bites the metal with two jaws. It grips edges, pipe and tube, and it will clamp onto non-magnetic metal like aluminum or stainless. Its weaknesses are weak springs after years of heat, small contact points and a tendency to be knocked off when you move a part.

A magnetic ground clamp holds with a flat face, so it can sit on a flat surface of a plate or a table. It’s quick to place and gives a larger contact patch on clean steel. It will not work on aluminum or 300-series stainless, and it needs a flat, clean surface; paint, rust or scale cause high resistance. Dirt, slag or spatter stuck to the face can also lower the pull.

Check the amp rating against your welder’s maximum output and the cable lug it accepts. An undersized clamp gets hot at the contact and can discolor or loosen. Look for a solid, copper-bearing connection point rather than a thin steel tab.

A practical setup for many shops: a magnetic clamp for flat steel work and tabletop use, plus a spring clamp for tubes, edges and non-ferrous metal. Whichever you use, clamp to bare metal, close to the weld, and never route current through bearings or a pivoting joint.

Locking pliers and C-clamps for welding

Clamps hold parts when a magnet can’t: thick stock, non-magnetic metal, or parts that need to be pulled flat. The basic classes are C-clamps, locking C-clamps, locking pliers with flat or sheet-metal jaws, and bar or quick-grip clamps.

Check these specifications before buying:

Locking C-clamps are quicker to set and release than screw C-clamps. They need a good adjustment before locking and can slip if the jaw faces are worn. A plain screw C-clamp gives the most controlled pressure. Plated or plain steel bodies are fine for shop use, and cast frames flex less under force than thin stamped ones. Clamps distort on heating, so don’t leave them tightly clamped on a part that will expand while you weld.

Fixture-table clamp compatibility: 16 mm vs 28 mm holes

A welding fixture table is a plate with a grid of holes. Clamps, stops and squares drop into those holes. Compatibility depends mainly on hole diameter. The two sizes buyers meet most are 16 mm and 28 mm. Some US tables use inch-based holes such as 5/8 in instead, so measure the table you have rather than assume.

The 16 mm size is common on lighter, smaller tables. The 28 mm size is common on heavier modular tables and carries bigger bolts and stronger clamp bodies. A 16 mm clamp pin won’t fit a 28 mm hole without an adapter, and a 28 mm pin won’t enter a 16 mm hole.

Before ordering, check:

A clamp set from one system is more likely to fit than a mixed set. Look at the stated hole size on each listing, not the table’s marketing name.

Is a fixture table worth it for a home or small fab shop?

A fixture table pays off when you repeat the same shape: gates, frames, brackets, tables, small trailers. It gives a flat, rigid reference, a grid for repeatable positions and many places to clamp. It’s less useful if you mostly do one-off repairs, or if your space can’t hold a table’s weight and footprint.

Money buys flatness, thicker plate, more precise holes and larger clamp ranges. A thinner or cheaper table can warp from heat and clamp load, which undermines the reason for owning one. A home-built bench with a steel top plus magnets and C-clamps can do much of the same job at lower cost, though without a hole grid for repeatable positions.

A sensible progression: start with a few 90° magnets, a magnetic ground clamp and a handful of locking C-clamps. Add a fixture table or a clamp set only when you find yourself rebuilding the same setup repeatedly and want to stop measuring every time.

Upkeep and common failure modes

Spatter is the main enemy. It fuses to magnet faces, clamp screws and table holes. Clean magnet faces with a wire brush and keep them flat; a burr or lump of slag raises the gap and drops pull. Anti-spatter spray or a screw cover on C-clamp threads reduces seizing. Clean table holes with a tap or a brush before pushing in a pin.

Watch for these problems:

Store magnets away from sensitive electronics and keep them dry to limit rust.

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FAQ

Can I use welding magnets on aluminum or stainless steel?

Not on aluminum, and not on common austenitic stainless like 304 or 316, because they are non-magnetic. Use C-clamps, locking pliers or a fixture table with clamps instead. Ferritic and martensitic stainless grades are magnetic, so check the specific alloy.

Is a magnetic ground clamp better than a spring clamp?

It depends on the work. A magnetic clamp is quick on flat, clean steel and gives a large contact face. A spring clamp works on edges, pipe and non-ferrous metal, and it won’t be affected by magnetic arc blow. Many shops keep both.

Do 16 mm and 28 mm fixture-table clamps interchange?

No, not directly. The hole diameter must match the clamp’s pin or bolt, and a 28 mm pin won’t enter a 16 mm hole. Measure your table’s holes and the pitch before ordering, and buy clamps from a set listed for that size.