Drilling Chart for Screw Sizes

Traditional Wood Screw vs.  Modern Production Screw

Although they require you to drill separate pilot and shank holes, many woodworkers still use the traditional screws in antique or reproduction pieces that call for matching hardware.

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. 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.

The difference between a traditional wood screw and a modern production screw is found in the sizing differences between the diameter of the screw shank and the screw threads.

Traditional Wood Screws - The shank diameter on this screw exactly matches the outside dimensions of the threads.  Threads on these screws are deeper near the point and begin to shallow as they get closer to the unthreaded shank or screw head.  Tapered drill bits are needed with this type of screw as the pilot hole should fit the outside shank diameter of the screw almost perfectly.  Creating this tight fit on traditional wood screws yields maximum holding power.

Modern Production Screws - The shank diameter is smaller than the major diameter but larger than the minor diameter.  The reduced shank diameter results in a deep thread profile offering great holding power.  Drilling a pilot with a straight drill bit yields excellent results because the shank of the screw is straight throughout its entire length.  The advantages of this are that straight bits do not require the same critical depth control as a tapered bit.

• Minor Diameter: Measurement of the body of the screw between the threads (one side to the other) – Smaller than major diameter and shank diameter
• Major Diameter: Measurement of the outside of the thread (one side to the other) – Larger than shank diameter and minor diameter
• Shank Diameter: Measurement of the bare shank (one side to the other) – Larger than minor diameter but smaller than the major diameter

Drill Bit Size Recommendations

In addition to their superior performance, McFeely’s 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 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 hold a drill bit up to the shank of the screw. The proper bit is the same size as the shank between the threads. Use a slightly larger bit for hardwoods and slightly smaller for softwoods.