Originally Posted by \./
What's it's purpose anyway?
Senior Member asking what a woodruff key is for? Seems kinda strange, but...
Woodruff keys are generally used in a coupling situation when you are mating a shaft to something (like a sprocket or gear for example). Their purpose is to lock the two items together so they move in unison, but also allow them to sheer apart to protect the equipment if the force on the union becomes to great. Thats why sometimes they are referred to a sheer key. They are sometimes rectangular on certain equipment but every one I have seen on a china 2-stroke motor has been the half moon type.
At a good hardware store (or Home Depot if you must) in the hardware isle (nuts/bolts/screws/etc) they usually have little boxes with drawer upon drawer of small hardware, screws, nuts, bolts, sheer keys etc. You should find half moon woodruff keys in there, plenty of variety in size. Best thing to do is compare an original key to the replacement to size, but if you don't have an original then buy a few that seem like the right size and see which one fits. (they should be cheap enough) There should be a size listed for the keys, china girls have all metric parts but you might not find metric keys in stock in the USA.
I have here a woodruff key I picked up at Home Depot (I think), the bag says "Woodruff Key" 3/32" X 3/8". This key fits nicely in my Grubee Skyhawk shafts....... (buy spares!)