Magnets can be fun

Magnets can be a fun addition to kinky play. Rare earth magnets are easily obtainable on popular auction sites but have one downside. Usually the issue with strong magnets is pulling them apart effectively as they are often thin flat and a smooth surface. I found a brand called Smeq whom have developed a system of enclosing the magnets into a torpedo shape for easily handling. This is the brand product I will speak of with my experience with magnetic play.
Some precautions to take when using strong magnets.
Never put them near electronic devices.
Be aware if the user has any metal plates or pace maker from past surgery
Never put them in your mouth or insert in any hole. If ingested or swallow, straight to A.E.
Don't let them bang together, this can causing chipping.
Don't leave them pinching an area of skin for prolonged periods of time to avoid skin damage.

Rare earth magnets are extremely brittle and often coated to stop them corroding. This is a main reason for not letting them bang together with great force as you will cause damage. They are the strongest magnetic material available and this is the technical stuff...
...Geek stuff...
Developed in the 1970s and '80s, rare-earth magnets are the strongest type of permanent magnets made, producing significantly stronger magnetic fields than other types such as ferrite or alnico magnets.
The magnetic field typically produced by rare-earth magnets can exceed 1.4 teslas, whereas ferrite or ceramic magnets typically exhibit fields of 0.5 to 1 tesla. There are two types: neodymium magnets and samarium-cobalt magnets.
The term "rare earth" can be misleading as these metals are not particularly rare or precious
You can read more geeky stuff about this in McCaig, Malcolm (1977). Permanent Magnets in Theory and Practice. USA: Wiley. p. 123.
The magnets I obtained from Germany came in a set of four and had their strength gauged by how much weight they could lift. Mine can carry around 1.5 kg each. They are fairly heavy for their size and the unique shape they are encased into makes it easy to pull them apart and apply without slipping through the fingers.

Magnets can be used for lots of uses in kinky play. With the strength of rare earth magnets the application possibilities are plentiful. The most common use is as a type of nipple clamp, labia, scrotum clamp and even on the nose or ear.
What ever area these little things have between them, the person wearing them has a slight discomfort then is mislead into a false sense of security. The magnets have a very tight connection but the body releases endorphin's to numb the discomfort. The person wearing them considers them to now be comfortable after a short time and goes about ones business.
The fun starts when you start to move the magnets around. This causes greater discomfort to the area of the body which is under stress and slight blood flow restriction. This minor restriction is stopping endorphins reaching the area and gets a very interesting result from slight movement.
When you finally remove the magnets, the minor amount of restricted blood to the area of skin rushes back along with the pain receptors kicking in depending how long the magnet was in place for. This causes a sharp pain followed by various amounts of pins and needles sensation.
The area of the skin is now sensitive for a short time for other uses such as flicking or prodding with items such as bamboo. I found the ear lobe to be very effective for this method and is a large flat surface of skin the magnets wont slip off easily. Nipple areas need pinching just behind the nipple to make them stay better with moment and just under the nose is would be for someone with a high pain threshold.
For using on private areas such as the labia or scrotum I would recommend a small barrier use to keep hygiene levels better. Normal rare earth magnets can be cleaned easily but the Smeq ones for example area a rotating ball with an enclosure which can pick up body fluids. The use of a snipped condom is an effective hygiene barrier during use and allow the magnets to work fine.
The trick is to explore different ways of using what ever size or type you have. When purchasing them be aware they are measured with N ratings. The higher the number such as N50 the stronger the magnet.