Creating precise stone seats is very easy when you use the Busch® 413AU style carbide burs.  The bur drills the perfect shape for the base of the facetted stone to ensure that it sits firmly. You will find the AU line of High Tech Carbide burs from Busch® will all cut more aggressively than standard carbides. Edges are more precise (making setting easier) and they produce a brighter finish.  Shanks measure 3/32" diameter and are marked with a gold band for easy identification.  Excellent for use on materials which are very hard and difficult to cut (such as platinum, white gold, titanium, and steel) while impressive for outstanding durability.  Please consult ANSI (American National Standards Institute) for speed recommendations. Made in Germany.