briggs flathead clutch bolt size

#1
I have a 3hp briggs and was wondering if someone could tell me the size of bolt I would need for the end of the shaft to hold clutch on. Ive always used a bolt and washer on the end of my other motors, but would a set screw in the clutch, alone, hold it on fine if I can't find a bolt at the hardware store?
Thanks guys
 
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