Little engineers will remember

Spark plug?

Aahh, the memories!

Pftt.. I still make fans with these using old reward cards and junk

you used to be able to buy upgrades from the hobby store, they did tend to fly into the wall more often though

I remember "performing tolerance tests" on these things. 3-6 volts was usually ok... more than that they get warm. Around the 9 volt threshold, they start to shriek.
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Needless to say, house current is a very, very bad idea. I tried that once. Once.

I always got my hair stuck in them.

I can recall people in school using these to make home made tattoo guns.