SHARS TOOLS #6 8 10 1/4-1/2 7pcs Cobalt Counterbore Set. Size: #6, #8, #10,1/4,5/16,3/8,1/2″ Pilot is oversize : #6 = Pilot 0.150″ #8=11/64 #10= 13/64 1/4 = 9/32″ 5/16= 11/32 3/8= 13/32 1/2= 17/32 shank size is 7/32″ 1/4″ 5/16, 3/8 and 1/2″. Used for expanding general rough hole or hole processing for bolts. Smooth chip flow and powerful cutting resistance because of 3 lips for regrinding. If you need to speak to a sales person feel free to call. We are open Monday through friday 8:30 to 5:00 est.