EMI protector?

[moeburn]

I bought this little 30c passive component, about the size of a cap, it looks like its a little coil of wire inside hollow ferrite, but it could just be plastic.  Its got a pin longer than the other, so i think its polarity-dependant.  IIRC, the bin said "EMI protectors".  Anyone know how to use it?

[nelson]

Electro magnetic interference protector.......would be my guess.