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Screw & Drill Bit Size Chart – Online Metric Imperial

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Screw & Drill Bit Size Chart

Complete reference for wood screws, metric & imperial machine screws with matching pilot holes, clearance holes, and tap drill sizes. Find the right drill bit for every screw.

Wood Screws

Pilot hole: 70-80% of root Ø (softwood)
85-95% of root Ø (hardwood)

Metric Machine Screws

Tap drill = Thread Ø − Pitch
Clearance hole = Thread Ø + 0.2~0.5mm

Imperial Machine Screws

UNC/UNF threads with numbered,
letter, & fractional drill bits

Screw Gauge Shank Ø (mm) Shank Ø (inch) Root Ø (mm) Pilot Softwood Pilot Hardwood Clearance Hole Typical Lengths
#22.20.0861.6 1.0 – 1.3 mm 1.3 – 1.5 mm 2.5 mm 6 – 19 mm
#32.50.0991.8 1.3 – 1.5 mm 1.5 – 1.8 mm 2.8 mm 6 – 25 mm
#42.80.1122.0 1.5 – 1.8 mm 1.8 – 2.0 mm 3.0 mm 10 – 32 mm
#53.20.1252.3 1.8 – 2.0 mm 2.0 – 2.3 mm 3.5 mm 12 – 40 mm
#63.50.1382.5 2.0 – 2.3 mm 2.3 – 2.5 mm 3.8 – 4.0 mm 12 – 50 mm
#73.80.1512.7 2.0 – 2.5 mm 2.5 – 2.7 mm 4.2 mm 16 – 60 mm
#84.00.1642.9 2.3 – 2.5 mm 2.5 – 2.9 mm 4.5 mm 16 – 75 mm
#94.50.1773.2 2.5 – 2.8 mm 2.8 – 3.2 mm 5.0 mm 20 – 80 mm
#105.00.1903.5 2.8 – 3.2 mm 3.2 – 3.5 mm 5.5 mm 20 – 100 mm
#125.50.2163.9 3.2 – 3.5 mm 3.5 – 3.9 mm 6.0 mm 25 – 120 mm
#146.30.2504.5 3.8 – 4.2 mm 4.2 – 4.5 mm 7.0 mm 30 – 150 mm
#167.00.2685.0 4.2 – 4.5 mm 4.5 – 5.0 mm 7.5 mm 35 – 180 mm
#187.50.2945.4 4.5 – 5.0 mm 5.0 – 5.4 mm 8.0 mm 40 – 200 mm
#208.00.3205.8 5.0 – 5.5 mm 5.5 – 5.8 mm 8.5 mm 50 – 250 mm

Pilot hole sizes are ranges. Use the smaller end for softwoods (pine, cedar) and the larger end for hardwoods (oak, maple). For very dense hardwoods, consider the upper range. Always test on scrap material first.

Screw Size Thread Ø (mm) Pitch (mm) Tap Drill (mm) Clearance Close (mm) Clearance Free (mm) Tap Drill (inch ref) Common Use
M1.61.60.35 1.25 1.8 2.0 #55 Small electronics
M22.00.40 1.6 2.2 2.4 #52 Electronics, hobbies
M2.52.50.45 2.05 2.7 2.9 #46 Small brackets
M33.00.50 2.5 3.2 3.4 #39 General light duty
M3.53.50.60 2.9 3.7 3.9 #32 Electrical fittings
M44.00.70 3.3 4.3 4.5 #30 Common assembly
M55.00.80 4.2 5.3 5.5 #19 Medium duty
M66.01.00 5.0 6.4 6.6 #8 General machinery
M88.01.25 6.75 – 6.8 8.4 9.0 H Structural, automotive
M1010.01.50 8.5 10.5 11.0 R Heavy machinery
M1212.01.75 10.2 – 10.3 12.5 – 13.0 13.5 13/32" Structural steel
M1414.02.00 12.0 14.5 – 15.0 15.5 15/32" Heavy structural
M1616.02.00 14.0 16.5 – 17.0 17.5 35/64" Heavy structural
M1818.02.50 15.5 18.5 – 19.0 19.5 39/64" Industrial
M2020.02.50 17.5 20.5 – 21.0 22.0 11/16" Industrial, large equipment
M2424.03.00 21.0 24.5 – 25.0 26.0 53/64" Large industrial

Tap drill sizes are calculated for standard coarse pitch (ISO metric). For fine pitch threads, use a larger tap drill. Clearance "close" fit is for precise alignment; "free" fit allows easier assembly with some play.

Screw Size Major Ø (inch) Major Ø (mm) TPI (UNC) Tap Drill Clearance Drill Tap Drill (mm) Clearance (mm)
#00.0601.5280 #56 (0.0465") #48 (0.076") 1.181.93
#10.0731.8564 / 72 #53 (0.0595") #44 (0.086") 1.512.18
#20.0862.1856 / 64 #50 (0.070") #42 (0.0935") 1.782.37
#30.0992.5148 / 56 #47 (0.0785") #37 (0.104") 1.992.64
#40.1122.8440 / 48 #43 (0.089") #33 (0.113") 2.262.87
#50.1253.1840 / 44 #38 (0.1015") #30 (0.1285") 2.583.26
#60.1383.5132 / 40 #36 (0.1065") #28 (0.1405") 2.713.57
#80.1644.1732 / 36 #29 (0.136") #18 (0.1695") 3.454.31
#100.1904.8324 / 32 #25 (0.1495") #9 (0.196") 3.804.98
#120.2165.4924 / 28 #16 (0.177") #2 (0.221") 4.505.61
1/4"0.2506.3520 / 28 #7 (0.201") F (0.257") 5.116.53
5/16"0.31257.9418 / 24 F (0.257") P (0.323") 6.538.20
3/8"0.3759.5316 / 24 5/16" (0.3125") W (0.386") 7.949.80
1/2"0.50012.7013 / 20 27/64" (0.4219") 33/64" (0.5156") 10.7213.10
5/8"0.62515.8811 / 18 17/32" (0.5312") 41/64" (0.6406") 13.5016.27
3/4"0.75019.0510 / 16 21/32" (0.6562") 49/64" (0.7656") 16.6719.45

TPI shown is for UNC (coarse) / UNF (fine). Tap drill listed is for UNC 75% thread engagement. For UNF threads, use a slightly larger tap drill. Numbered drills #1-#60, letter drills A-Z.

Pilot / Softwood Pilot / Hardwood Clearance Hole Tap Drill Highlighted = Search Match

Frequently Asked Questions

What is a pilot hole and why do I need one?
A pilot hole is a small-diameter hole drilled before driving a screw, primarily used in woodworking. It serves three essential purposes: (1) Prevents wood splitting — especially crucial near edges and in hardwoods; (2) Guides the screw — ensuring it drives straight and true; (3) Reduces driving torque — making it easier to drive the screw without stripping the head. For softwoods, the pilot hole should be approximately 70–80% of the screw's root diameter. For hardwoods, use 85–95% to prevent snapping the screw.
What's the difference between a pilot hole and a clearance hole?
A pilot hole is drilled into the bottom piece (the piece the screw threads bite into) and should be slightly smaller than the screw's root diameter so the threads can grip. A clearance hole is drilled through the top piece (the piece being fastened down) and should be slightly larger than the screw's shank diameter, allowing the screw to pass through freely without threading into the top piece. This combination ensures the two pieces are pulled tightly together.
How do I choose the right drill bit for a metric machine screw?
For metric machine screws, the tap drill size = Thread Diameter − Pitch. For example, an M6×1.0 screw: 6mm − 1.0mm = 5.0mm tap drill. This formula gives approximately 75% thread engagement, which is optimal for most applications. For the clearance hole (through-hole), add 0.2–0.5mm to the thread diameter for a close fit, or 0.5–1.0mm for a free fit. Always refer to the chart above for exact values.
What do numbered and letter drill bits mean?
In the imperial system, drill bits come in three naming conventions: Fractional (e.g., 1/4", 3/8"), Numbered (#1 through #80, where higher numbers are smaller — #80 is 0.0135" while #1 is 0.228"), and Letter (A through Z, where A=0.234" and Z=0.413"). Numbered and letter drills fill the gaps between fractional sizes for precision work. For example, a #7 drill (0.201") fits between 3/16" (0.1875") and 13/64" (0.2031").
Why do hardwood and softwood need different pilot hole sizes?
Hardwoods (oak, maple, walnut) are denser and less compressible than softwoods (pine, cedar, fir). A pilot hole that's too small in hardwood can cause the screw to bind, overheat, and snap. The denser material resists thread penetration, so a slightly larger pilot hole (85–95% of root diameter) is needed to reduce friction while still providing strong grip. Softwoods, being more compressible, can accommodate a smaller pilot hole (70–80%) without splitting.
Can I use this chart for self-tapping or self-drilling screws?
Self-tapping and self-drilling screws are designed to create their own threads (and sometimes their own hole) in materials like sheet metal, plastic, or thin steel. They generally do not require a pre-drilled pilot hole — that's their main advantage. However, for thicker or harder materials, a small pilot hole (about 70% of the screw diameter) can still help with alignment and reduce driving effort. Always check the manufacturer's specifications for the specific screw type you're using.
What is a countersink and when should I use one?
A countersink is a conical recess cut into the surface of a material that allows a flat-head or countersunk screw to sit flush with (or below) the surface. Countersink drill bits typically have an 82° or 90° angle to match common screw head angles. Use a countersink when you want a smooth, professional finish — for example, in furniture making, cabinetry, or anywhere the screw head should not protrude. After countersinking, you can fill the recess with wood putty for an invisible finish.
How accurate are online screw-to-drill-bit charts?
Online charts provide excellent general guidance based on industry standards (ISO, ANSI, DIN). However, the optimal drill size can vary slightly depending on: material composition (some exotic hardwoods behave differently), screw manufacturer (minor variations in thread geometry), environmental conditions (humidity affects wood), and specific application requirements. We recommend testing on a scrap piece of the same material before drilling into your final workpiece. This chart is accurate for standard fasteners from major manufacturers.
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