Our Timber Framing Countersink Kit is a long drill bit and a countersink cutter for seating GRK structural screws cleanly in timber frame floor joists.
The 1/4 x 12 in high speed steel bit, with a 9 in flute, drills the pilot deep enough for long structural screws, and the 3/4 in Type X countersink cutter, a four-blade high speed steel cutter from W.L. Fuller, cuts the recess so the head sits flush.