stage one I believe is OEM, original equipment. stage two has a bit more material on the disc, stage three has more material, it may also require the disc to be HOT before it clamps property to the plate.
Could you be more particular as to what kind of car/bike/quad your talking about. If it is GM they have oth OEM and performance parts they put in different styles of cars. Do you have a hydaulic or mechanical clutch? Need more information