Drill Bit Size Recommendations

Tapered vs Straight Drill Bits

Many people use tapered drill bits to drill both the body hole and the pilot hole in one pass for their wood screws. As those who use them can attest, depth control using tapered threads is critical - too deep and the threads won’t hold, too shallow and the screw becomes jammed. Even worse, tapered bits are rather expensive.

In addition to their superior performance, Square Drive screws are also easier to install than most “garden variety” hardware store screws. Because the screw shank is straight throughout its entire length, (except for the point), drilling a pilot with a straight drill bit yields excellent results. The reduced shank diameter at the head means an enlarged body hole isn’t necessary. Finally, the straight bit doesn’t require the critical depth control needed with a tapered bit.

Now, if you’re still using the old style slotted or phillips drive wood screws, tapered shank drill bits are the only way to go; they fit the profile of the screw almost perfectly, yielding maximum holding power. Because they drill the proper size hole for both the shank and the threaded portions of the screw, drilling pilot holes is a one-step process.

Drill Bit Size Recommendations

Drill bit selection for square drive screws, or any other fastener, should take into consideration the material properties. In general, the harder the material, or the softer the screw, the larger the pilot hole should be. Use the following table as a starting point. If in doubt, a quick and relatively safe technique is to simply hold a drill bit up to the shank of the screw. Nominally, the proper bit is the same size as the shank between the threads. In practice, use a slightly larger bit for hardwoods, slightly smaller for softwoods.

Pilot Drill Size Recommendations For Square Drive Screws
(Use Brad or Standard Point Drill Bits)

Pilot Drill Size Recommendations For Standard “Wood Screws”
(Using Taper Point Drill Bits)

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