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Drilling near the edge of a board leaves little wood to hold a screw. A pilot hole that is too small can split the board; one that is too large can leave the screw with little grip. The right hole depends on the screw’s shank, the wood, and how close the hole is to the edge—not just on a general drill-bit chart.
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Choose the location before drilling
Measure from the board’s edge to the center of the screw hole. As a practical starting point, keep the center at least twice the screw’s major diameter from the edge. For a 1/4-inch screw, that means about 1/2 inch. Dense hardwood, a narrow board, or a large screw may need more clearance. Softwood can tolerate less, but it can still split, especially near the end of a board.
If the joint allows it, move the screw inward, use a shorter or thinner screw, or add a second piece of wood to increase the fastening area. These changes are often more reliable than trying to rescue a hole placed too close to the edge. Avoid drilling into a visible end-grain crack or a knot; both make splitting more likely.
Match the bit to the screw
For a typical wood screw, the pilot hole should be close to the screw’s root diameter—the diameter of the solid center beneath the threads. The screw threads need to bite into the wood, so a hole as wide as the thread tips can weaken the hold. In hardwood, use a pilot hole closer to the root diameter; in softwood, a slightly smaller hole may work, but it raises splitting risk near an edge.
Check the screw’s package for a pilot-hole chart if one is provided. Otherwise, compare the screw with drill bits: hold the bit in front of the screw and choose one that hides the screw’s core while the outer threads remain visible on either side. This is a useful estimate, not a substitute for a test in scrap wood. If you are buying a bit set for occasional repairs, a wood drill bit set is usually adequate; a single correctly sized bit is fine if you already know the screw size.
| Situation | Pilot-hole choice | Main trade-off |
|---|---|---|
| Softwood, screw well away from edge | Near the screw’s root diameter, sometimes slightly smaller | Smaller hole gives strong thread bite but needs more driving force |
| Hardwood or hole close to edge | Near the root diameter; do not undersize to force extra grip | Reduces splitting and screw breakage, while threads still engage |
| Large screw or deep fastening | Use the screw maker’s chart or test in scrap | Guessing can leave the screw stuck, snapped, or loose |
Drill a straight, controlled hole
Mark the center with a pencil, then make a small indentation with an awl or a nail. That helps keep the bit from skating toward the edge. Clamp the work if possible, and place scrap wood beneath it if the bit may break through the far side. Fit a sharp twist bit or brad-point bit; a brad-point bit starts neatly in wood, while an ordinary sharp twist bit is cheaper and works well for occasional holes.
Use a drill rather than an impact driver to make the pilot hole. A cordless drill gives better control at low speed and is less likely to jerk when the bit catches. A cordless drill/driver is a sensible general-purpose choice; a hammer drill is unnecessary for wood. Set the clutch aside or use drill mode, hold the tool square to the surface, and start slowly. Keep steady pressure, but do not force the bit. Pull the bit out briefly if chips clog the flutes, then continue to the required depth.
Make the pilot hole about as deep as the threaded portion that will enter the first piece of wood. A piece of tape on the bit is a simple depth mark. If the screw passes through one board before biting into another, the first board may also need a clearance hole wide enough for the screw shank. That lets the screw pull the boards together instead of threading into both and leaving a gap.
Drive the screw without splitting the edge
For a countersunk screw, use a countersink bit or a shallow, wider recess so the head sits flush without wedging the wood apart. Do not make the pilot hole larger at the surface and assume that will prevent splitting; the narrow part of the hole must still be correctly sized and centered.
Drive the screw at low speed with a drill/driver, keeping the bit firmly seated in the screw head. Stop when the head is seated. Overdriving can crush fibers, strip the recess, or split the edge even after careful drilling. An impact driver is useful for many long or repeated fastenings, but its rapid blows make it easier to overdrive a small edge fastening. If using one, select a low setting if available and ease off as the head approaches the surface.
If the wood starts to split
Stop immediately rather than driving the screw harder. Back it out, then inspect the hole and the edge. A split that runs to the edge may mean the screw has little dependable holding strength. For a non-structural repair, you may be able to move the screw, use a smaller screw, or clamp and glue the split before refastening after the glue cures. For a load-bearing joint, replace the damaged piece or redesign the fastening rather than relying on a glued crack.
If the screw turns without tightening, the pilot may be too large, the wood may be damaged, or the screw may not have enough threaded length in the receiving piece. Move to fresh wood and use an appropriate screw; filling the hole with a loose sliver is not a dependable fix. For an uncertain screw size, drill a test hole in offcut material of the same species and thickness, then drive the screw and check that it seats without splitting or spinning freely.