possibly looks something like this
http://motorcycleproducts.co.uk/cata...8a4d8998c405f9 it is used to retain gearing-pulley's etc on shafts such as crank shafts,camshafts
there is a "keyway" located on the shaft and pulley or gear the woodruff key simply lines everything up and shouldnt allow anything to slip-but in the event of a key failure-its usually a big "ouch"
every one beat me to it
hope you get it sorted
[Edited on 6-7-2005 by monstermob 998]