What Size Drill Bit for #8 & #10 Screw? Pilot Hole Size Chart (2024)

Drill bits come in a wide range of sizes to ensure each project can get completed with precision. Each one uses a different naming convention to promote accuracy, including letters, numbers, and fractions.

When you measure drill bits infractions, all of them are a component of 64ths. That means the smallest one is 1/64, while the largest size is 63/64. You would then reduce them to the lowest fractional equivalent: a 2/64 bit would actually be a 1/32.

You’ll also see numbers that go from 1-80, with the largest number being the smallest drill bit.

When you select the drill bit size for #8 or #10 screws, several different features must be part of that choice. You must account for the screw type, the materials used, and the thread design.

Pilot Hole Drill Bit Size Chart

What size drill bit should you use for pilot holes for wood screw? This handy pilot hole size chart should help you.

Why Pre-Drill a Pilot Hole?

Since screws have a sharp end to them, why is it necessary to pre-drill holes to accommodate the fastener?

It is true that the self-tapping screws can easily penetrate into softwood with the help of a drill driver or an impact driver. However, when it comes to larger diameter holes and tough materials such as hardwood and metal you will need to drill pilot holes. These pilot holes make it much easier to place the screw in the correct location. When you have multiple boards to fasten, this work guarantees that the materials won’t crack or the screw breaks off while working.

When threading thick metal plates, you must drill the hole to the size of core diameter and use a threading tap.

When you work with hardwoods, the pilot hole should be the size of the screw’s “minor diameter.” It can be slightly smaller for softer woods.

If you skip the pilot hole (or drill one that isn’t large enough), inserting the screw can cause hairline cracks to form in the material. This problem is especially prevalent in MDF, plywood, and engineered products, but it can also occur in solid wood.

Although you might not see the cracks at first, they can eventually widen as the installation ages. If given enough time, your wood joint or fastening work will ultimately fail.

Enlarge the Pilot Hole in a Top Board

If you fasten two wood products, try to make the pilot hole more extensive in the top board than the bottom one. This design makes it easier for the screw to pull the items together.

For this step, the clearance hole should be at least the size of the major diameter for the screw.

When this step gets skipped, you’ll often see a small gap between the two boards or surfaces jointed together. Depending on what you’re making, glue could seal the bond with this result, but it isn’t effective if your spacing is larger than the thickness of a standard sheet of printer paper.

What Size Drill Bit for a #8 Screw?

If you have type A, AB, or B self-tapping screws or type 25 thread-cutting screws, you’d need a #29 drill bit for your pilot hole.

When you have high-low thread-forming screws, the suggested drill bit for a #8 screw is the #30 for materials with a flexural modulus of more than 200,000 PSI. If you have materials that rate under that figure, a #31 drill bit is a better choice.

If you are using #8 hammer drive or U-drive screws, your pilot hole’s recommended drill bit size is #27.

Are you working with plastic materials? Some thread-forming screws for it or alternatives like PLASTITE® require a pilot hole diameter of 0.1490 or 0.1580 for soft or brittle items, respectively.

When you need to use standard wood screws for your project, the straight size is 1/8-inch for the #8 screw. If you need a tapered result, an 11/64-inch bit works better for hardwood, while a 5/32-inch bit is perfect for softwood. You’d use a C8 countersink.

What Size Drill Bit for a #10 Screw?

If you have type A, self-tapping screws, type AB self-tapping screws, type B self-tapping screws, or type 25 thread-cutting screws, you’d need a #21 drill bit for your pilot hole.

When you have high low thread forming screws, the suggested drill bit for a #10 screw is the #27 for materials with a flexural modulus of more than 200,000 PSI. If you have materials that rate under that figure, a #29 drill bit is a better choice.

If you are using #10 hammer drive or U-drive screws, the recommended drill bit size for your pilot hole is #20.

When your project uses hardwood or softwood, a standard #10 wood screw is suitable for the fastening work. You’d use a 9/64-inch bit for a straight pilot hole, although some softwoods might benefit from having a 1/8-inch bit.

If you need a tapered pilot hole for your project, hardwoods would need a 13/64-inch bit, while softwoods would use a 3/16-inch bit for the #10 screw. You’d want to use a C102 countersink.

Once you have the equipment ready, it helps to clamp your boards gently to ensure they don’t move. Drill from a completely vertical or horizontal position to create an accurate pilot hole. After that work is finished, you can place the #8 or #10 screw with precision to make a firm bond.