A screw size chart is an essential workshop reference that shows major diameter, thread count, and — most importantly — the correct pilot hole size for each screw gauge. Drilling the right pilot hole prevents wood from splitting, reduces driving force, and ensures maximum holding strength. This chart covers wood screws, machine screws, and sheet metal screws with both inch and metric values.
Wood Screws
| Gauge | Major Dia | Pilot – Softwood | Pilot – Hardwood |
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Head Types
Drive Types
How to Use the Screw Size Chart
This screw size chart covers the three most common screw types used in woodworking, metalworking, and general construction: wood screws, machine screws, and sheet metal screws. Each table shows major diameter, pilot hole requirements, and thread specifications so you can select the right drill bit before driving any fastener.
Step 1: Select the Screw Type Tab
Click Wood Screws, Machine Screws, or Sheet Metal Screws to filter the chart to the type you are working with. Wood screws have tapered shanks and are designed to pull two pieces of wood together. Machine screws have uniform cylindrical shanks and mate with nuts or tapped holes. Sheet metal screws are self-tapping and designed to cut threads into thin metal or plastic.
Step 2: Search by Gauge or Size
Type a gauge number (e.g., #8) or size designation (e.g., 1/4-20) into the search box. The active table filters in real time. This is especially useful when you already have a screw and need to identify the correct pilot drill without scanning the entire table.
Step 3: Toggle Inches or Millimeters
Use the in / mm toggle to switch all diameter values between inches and millimeters. Fractional inch pilot hole sizes (like 7/64") are shown as-is in imperial mode. In metric mode, all values are shown as decimal millimeters for easy matching with metric drill sets. The major diameter and pilot hole sizes both convert simultaneously.
Pilot Holes for Wood Screws
Wood screw pilot holes are listed separately for softwood (pine, cedar, fir, poplar) and hardwood (oak, maple, walnut, birch). Softwoods compress under load, so a slightly smaller hole still allows the screw to cut through cleanly. Hardwoods resist compression and require a larger pilot hole to prevent splitting and reduce driving torque. Always pre-drill hardwood with the hardwood column size, especially near edges and end grain.
Tap Drill Sizes for Machine Screws
Machine screw tap drill sizes are numbered or lettered drill bits from the US wire gauge and letter drill standards. A tap drill creates the right minor diameter so a tap can cut clean threads with approximately 75% thread engagement — the industry standard for good holding power without excessive tap stress. Coarse thread (lower TPI) tap drills are slightly larger than fine thread drills of the same nominal size, because coarse threads have a larger pitch and remove more material per revolution.
Choosing the Right Head and Drive
Use the Head Types and Drive Types reference panels to match the screw style to your application. For flush installations in wood, choose a flat head (countersunk) screw with a countersink bit. For maximum torque without cam-out, Torx or square drive are the best choices. For structural metal-to-metal applications, hex head cap screws tightened with a wrench provide the most reliable clamping force.
FAQ
Is this screw size chart free to use?
Yes, this screw size chart is completely free. It runs entirely in your browser — no signup, no account, and no data is sent to any server. Bookmark it for quick shop reference anytime.
Is my data private when using this tool?
Yes, all lookups happen locally in your browser. No data is transmitted to any server. The tool works entirely offline once the page is loaded.
What is a pilot hole and why does it matter?
A pilot hole is a small pre-drilled hole that guides the screw and prevents wood from splitting. Using the correct pilot hole size reduces driving torque, avoids material damage, and ensures the screw threads grip properly. Too small and the wood may split; too large and the screw loses holding power.
Why are there different pilot hole sizes for softwood vs hardwood?
Hardwoods are denser and more resistant to compression, so they need a slightly larger pilot hole to prevent the wood fibers from binding on the screw shank or causing splits. Softwoods compress more easily, requiring a smaller pilot hole to still achieve a secure bite.
What is the difference between coarse and fine thread machine screws?
Coarse thread (lower TPI — threads per inch) bites into material faster, is easier to start, and is better for softer materials and general use. Fine thread (higher TPI) provides greater clamping force, is less likely to loosen from vibration, and is preferred for harder materials and precision assemblies.
What do the tap drill sizes like #43 or F mean for machine screws?
Numbered and letter drill sizes are US wire gauge and letter drill standards used before decimal-inch or metric drill sizes became common. A #43 drill is 0.089 inches in diameter. Letters run from A (0.234 in) to Z (0.413 in). These sizes correspond to the minor diameter of the thread, leaving the right amount of material for the tap to cut clean threads.
How do I choose the right screw length?
A general rule is that at least half the screw length should penetrate into the base material. For wood-to-wood joints, 1-inch penetration into the lower piece is a common minimum. For sheet metal and machine screws, thread engagement of at least 1.5× the major diameter is recommended for reliable pull-out strength.
What head types work best for different applications?
Flat head screws sit flush with or below the material surface — ideal for finish work. Pan head and round head screws sit above the surface, distributing load over a wider area. Hex head and socket head cap screws allow higher torque for structural applications. Truss heads offer a large bearing surface for soft materials like foam or plastic. Choose the head type based on whether you need flush fit, high torque, or load distribution.