Originally posted by westcoaststyle
It doesn't actually 'hold on' your pulley - the bolt does that. The crank pulley has a notch in it and slides over this key so that it turns with the crank. Without this, the pulley wouldn't turn with the crank.
Get it?
Just trying to keep it simple. That key is mostly there to hold the pulley on the crank on the assembly line until it gets to the station with the impact. The crank bolt probably puts enough force on the pulley to hold it there without the key.