Countersink Bits: #8 vs #10 and When to Use Each
By Premium CNC & Router Bits for Precision Cutting | Published: 2026-10-31
Category: Comparisons
Compare Whiteside #8 and #10 countersink bits by screw size, pilot diameter, and cutting width so you can choose the right bit for clean, flush wood screw heads.
Quick answer
Choose the #8 countersink for #8 wood screws and the #10 countersink for #10 screws. The #10 has a wider 1/2-inch cutting diameter and a larger 13/64-inch pilot bore, while the #8 uses a 3/8-inch cut and an 11/64-inch pilot.
Why the screw size decides the bit
A countersink bit does two jobs at once: it bores a pilot hole for the screw shank and cuts the angled seat that lets the head sit flush. If the pilot is too small for the screw, the wood can split; if the seat is too narrow, the head stands proud. The #8 and #10 bits are matched to those two screw sizes, so the screw box is your first reference, not the bit drawer.
The trade-off: one bit per screw size, not one bit for all
The #10 bit cuts a wider seat and a larger pilot than the #8, which suits thicker #10 screws but is oversized for #8 screws. Using the #10 on a #8 screw can leave a loose pilot and a seat wider than the head needs. The #8 is the reverse: correct for #8 screws, but too small to accept a #10 shank. Neither bit covers both sizes, so the real choice is which screw size dominates your work.
What the catalog does not tell you
Both bits are listed with an 82-degree angle, high-speed steel construction, four flutes, and a 1/2-inch outside cutting diameter for the #10 or 3/8-inch for the #8. The catalog does not list shank diameter, overall length, or recommended RPM, so check those against your drill or drill press before ordering if clearance matters. Replacement tapered bits are listed for both, which helps when the pilot drill wears before the cutter.
Trade-offs at a glance
- Screw size match: Use the #8 bit for #8 wood screws and the #10 bit for #10 wood screws. Match the bit to the screw label rather than to the hole you already drilled. If a project mixes screw sizes, keep both bits on hand rather than forcing one to cover both.
- Pilot diameter: The #8 bit has an 11/64-inch inside diameter; the #10 has a 13/64-inch inside diameter. These are sized for their matching center drills and screw shanks. Confirm your screw shank fits the pilot before drilling a full run of holes.
- Cutting width: The #8 cuts a 3/8-inch diameter seat; the #10 cuts a 1/2-inch seat. The wider #10 seat supports a larger screw head but removes more surface wood. On thin or fragile stock, the smaller #8 cut leaves more material around the hole.
Product facts
- Whiteside #10 Countersink Bit: 4-flute, 82-degree adjustable #10 countersink with 1/2-inch outside cutting diameter and 13/64-inch inside diameter for a 13/64-inch center drill. The wider cut and larger pilot match #10 screw shanks, so the head seats flush without an oversized pilot for that screw size.
Whiteside #10 Countersink Bit - Whiteside #8 Countersink Bit: 4-flute, 82-degree adjustable #8 countersink with 3/8-inch outside cutting diameter and 11/64-inch inside diameter for an 11/64-inch center drill. The smaller seat and pilot suit #8 screws, reducing the chance of a loose fit or a seat that extends beyond the screw head.
Whiteside #8 Countersink Bit
Which bit fits your work
Best for
- #8 wood screws in furniture, cabinets, and general assembly
- Projects where a smaller 3/8-inch countersink suits thin or narrow stock
- Users who want a dedicated bit for a single common screw size
Not for
- #10 screws, which need the larger 13/64-inch pilot and 1/2-inch seat
- Mixed-size screw projects where one bit must cover both #8 and #10
- Applications requiring a shank size or RPM rating not listed in the catalog
