This 3-flute flat bottom counterbore drills a pilot hole and cuts a flat-bottomed counterbore in a single pass -- the flat bottom (unlike a countersink's angled cone) is sized for lag screws, lag bolts, washer-head screws, T-nuts, and other fasteners that need a flush-seating flat washer or head. The pilot drill is a TiN-coated twist drill for added wear resistance. It's available in 17 drill/counterbore combinations.
- Drill/counterbore sizes range from 1/8" drill x 3/8" counterbore up to 1/2" drill x 1" counterbore
- TiN-coated twist drill bores the pilot hole ahead of the 3-flute counterbore cutter
- 1/4" hex power bit shank fits quick-change chucks
- One-pass operation -- no separate pilot-drilling and counterboring steps
Match the combination to your fastener's shank and head diameter, then drill straight through in one pass for a flat-bottomed recess the head or washer will seat into flush.