Tapper™ Drill Bits in the diameters listed are nominal size. 3/16" and 1/4" Perma-Seal™ Tapper™ anchors must be installed with special tolerance Tapper™ drill bits. 1/4" Stainless Steel Tapper™ anchors require the use of specific tolerance Tapper™ drill bits, which are gold or silver colored, to denote the standard size and special application size for harder materials. 3/8" diameter Tapper™ anchors should be installed with a 1/4" ANSI drill bit.