The steel cup of cup magnets let the magnetic force concentrate on one magnetic surface. With the protection from steel cup, the inner magnet can be used much longer time. External(male) thread stud can be made on the top of steel cup, that is external thread stud cup magnets. Both neodymium discs and ferrite discs can be used in external thread stud cup magnets. Neodymium cup magnets with external(male) thread stud have stronger magnetic force, but they are more expensive than ferrite external thread stud cup magnets.
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