The first cone will be slightly smaller than the second cone. The first cone makes the outline of the thread thinner, and the second cone makes the thread smoother on the basis of it, so that the screw can be easily screwed in. Mainly depends on the difference in the head. A nose cone usually grinds down five teeth. Two cones grind off two teeth. Mainly a cone that is easy to cut. Two cones can process three teeth that one cone can't.