Why are pot magnets so strong?
Short answer: a pot magnet is a neodymium magnet in a steel pot. The steel redirects the field from the back and sides to the front, so almost all the force ends up on one face. As a result, a pot magnet on thick steel is often 2 to 4 times stronger than a loose magnet of the same diameter: a Ø20 mm pot magnet holds approx. 16 kg, a Ø20 x 5 mm disc magnet approx. 4.9 kg. Downside: the force drops off faster with an air gap or on thin steel.
Pot magnet versus loose magnet: our figures
| Diameter | Loose disc magnet (N48) | Pot magnet |
|---|---|---|
| Ø20 mm | Ø20 x 5 mm: 4.9 kg | Ø20 x 7 mm: 16 kg |
| Ø25 mm | Ø25 x 5 mm: 5.3 kg | Ø25 x 8 mm: 18 kg |
| Ø32 mm | Ø30 x 5 mm: 5.5 kg | Ø32 x 8 mm: 29 kg |
| Ø40 mm | Ø40 x 10 mm: 20 kg | Ø40 x 8 mm: 72 kg |
Holding force according to our product specifications, measured perpendicular on thick steel. See also hook magnet or eye magnet for the pot dimensions.
How does the steel pot work?
A loose magnet has two poles: the field comes out at the front and runs back through the air to the back. Much of that field is not used. In a pot magnet the back sits against the steel base; the steel guides the field via the rim of the pot to the front. The front then has one pole in the centre and the other at the rim. The field closes through the steel you place the magnet on: a short, closed magnetic circuit. That is why the holding force is high and the back is hardly magnetic.
When does a pot magnet reach its full force?
- Thick steel: at least 5 – 10 mm for pot magnets from Ø32 mm. On a 1 mm steel plate you sometimes only get a quarter.
- Full contact: the whole face must lie flat on the steel. Paint, rust or 1 mm of distance can halve the force or worse.
- Perpendicular load: sideways, a pot magnet already slides at 15 – 25% of its holding force. A rubber casing or rubber protective pad gives more grip.
Which pot magnet suits your application?
- Hanging from a hook or eye: hook magnets and eye magnets
- Screwing with a bolt: pot magnet with threaded stud or threaded bush
- On paintwork or a car: rubber pot magnets
- Retrieving objects from water: fishing magnets
A selection guide by mounting and holding force is in which pot magnet should you choose?
Frequently asked questions
Why is the back of a pot magnet hardly magnetic?
The field is guided to the front by the steel pot. That means you can place a pot magnet against a steel beam without the back attracting anything.
Does a pot magnet work through wood or glass?
Less well than a loose magnet: the short field drops off quickly with distance. Through a panel, it is better to choose two loose magnets. See do magnets work through wood, glass and plastic?
Can a pot magnet stick to another magnet?
Yes, at the front, but it is designed for steel. Two pot magnets against each other pull less strongly than a pot magnet on thick steel.
Read also
- Which pot magnet should you choose?
- How is holding force determined?
- Disc, block, ring or pot magnet: what is the difference?
Need help choosing? Use the Magnet Advisor or contact us.
