1 x 4" Magnet: 50 lbs (22.7 kg) pull force.
4 x 3" Magnets: 25 lbs (11.3 kg) pull force each.
2 x Mini Magnets: 10 lbs (4.5 kg) pull force each.
Ferrous Metals Only: These only work on iron-based (magnetic) metals like steel; they will not work on aluminum or copper. [1]
Heat Sensitivity: Magnetic tools can lose their strength if exposed to extreme heat for too long. Use them for tack welding, and then remove them for final, high-heat passes.
Pinch Hazard: The strong magnetic pull can easily pinch fingers between the tool and a workpiece. Always handle them with care.