Screw Size Chart
The Screw Size Chart is a reference tool covering screw size chart, screw size guide, screw size chart metric, wood screw size chart. Use the chart below to look up values instantly. Printable and downloadable versions are available on this page.
Wood Screw Size Chart
| Screw Gauge Number | Shank Diameter (inches) | Shank Diameter (mm) | Common Lengths Available | Typical Use |
|---|---|---|---|---|
| #2 | 0.086" | 2.18 mm | 1/4" to 3/4" | Small hinges, lightweight cabinet hardware |
| #4 | 0.112" | 2.84 mm | 3/8" to 1" | Light-duty hinges, small hardware, toy assembly |
| #6 | 0.138" | 3.51 mm | 1/2" to 2" | General light-duty woodworking, cabinet doors |
| #8 | 0.164" | 4.17 mm | 5/8" to 3" | Most common general-purpose size. Furniture, decking, trim |
| #10 | 0.190" | 4.83 mm | 3/4" to 3.5" | Heavier joinery, structural connections in wood |
| #12 | 0.216" | 5.49 mm | 1" to 4" | Heavy-duty woodworking, structural framing |
| #14 | 0.242" | 6.15 mm | 1" to 4" | Large structural fasteners |
| #16 | 0.268" | 6.81 mm | 1.5" to 5" | Heavy structural applications |
| 1/4" | 0.250" | 6.35 mm | 1" to 6" | Treated lumber, structural bolting |
| 5/16" | 0.313" | 7.94 mm | 1.5" to 6" | Heavy structural and lag bolts |
Source: ASME B18.6.1 wood screw standard
Machine Screw Size Chart
| Size Designation | Major Diameter (inches) | Threads Per Inch (UNC coarse) | Threads Per Inch (UNF fine) | Tap Drill Size (UNC) |
|---|---|---|---|---|
| #0-80 | 0.060" | n/a (only fine) | 80 | #56 |
| #1-64 | 0.073" | 64 | 72 | #53 |
| #2-56 | 0.086" | 56 | 64 | #51 |
| #3-48 | 0.099" | 48 | 56 | #47 |
| #4-40 | 0.112" | 40 | 48 | #43 |
| #5-40 | 0.125" | 40 | 44 | #38 |
| #6-32 | 0.138" | 32 | 40 | #36 |
| #8-32 | 0.164" | 32 | 36 | #29 |
| #10-24 | 0.190" | 24 | 32 | #25 |
| #12-24 | 0.216" | 24 | 28 | #17 |
| 1/4"-20 | 0.250" | 20 | 28 | #7 |
| 5/16"-18 | 0.313" | 18 | 24 | F |
Source: ASME B1.1 Unified Screw Threads standard
Metric Screw Size Chart
| M Designation | Nominal Diameter (mm) | Standard Pitch (mm) | Tap Drill Size (mm) |
|---|---|---|---|
| M2 | 2 mm | 0.40 mm | 1.60 mm |
| M2.5 | 2.5 mm | 0.45 mm | 2.05 mm |
| M3 | 3 mm | 0.50 mm | 2.50 mm |
| M4 | 4 mm | 0.70 mm | 3.30 mm |
| M5 | 5 mm | 0.80 mm | 4.20 mm |
| M6 | 6 mm | 1.00 mm | 5.00 mm |
| M8 | 8 mm | 1.25 mm | 6.80 mm |
| M10 | 10 mm | 1.50 mm | 8.50 mm |
| M12 | 12 mm | 1.75 mm | 10.20 mm |
| M16 | 16 mm | 2.00 mm | 14.00 mm |
Source: ISO 261 metric screw thread standard
Screw Head Types Reference
The screw head type determines the tool required to drive it and affects the appearance and holding strength of the fastened joint.
| Head Type | Driver Required | Common Applications |
|---|---|---|
| Phillips (#1, #2, #3) | Phillips screwdriver | General-purpose — the most common head in consumer products |
| Slotted (flat head) | Flat blade screwdriver | Older hardware and decorative screws. Less common in modern use |
| Torx (T10, T15, T20, T25, T27, T30) | Torx or star driver | Automotive, electronics, and appliances. Better cam-out resistance than Phillips |
| Square (Robertson) | Square tip driver | Common in Canada. Excellent cam-out resistance |
| Hex socket (Allen) | Hex key or Allen wrench | Furniture flatpack, bike components, and machinery |
| Pozidriv | Pozidriv driver (not Phillips) | European alternative to Phillips — more contact surface |
| Security Torx (Tamper-resistant) | Security Torx driver with centre pin hole | Appliances, electronics, public fixtures where tampering prevention is needed |
| Combination (Phillips and slotted) | Phillips or flat blade | Versatile — accepts either driver type |
Screw Size Converter
Enter a screw gauge (#4, #6, #8 etc.) or metric size (M3, M4, M5) to get the diameter in mm and inches, recommended pilot hole sizes, and equivalent sizes.
Frequently Asked Questions
What is the most common screw size?
#8 gauge wood screws in lengths from 1" to 3" are the most commonly used screws in general woodworking and DIY. They strike the best balance between holding strength and ease of driving in most wood types.
What does M6 x 1.0 mean?
M6 means a metric screw with a nominal diameter of 6 mm. The 1.0 refers to the thread pitch — the distance between threads in millimetres, in this case 1.0 mm between each thread.
What is the difference between UNC and UNF threads?
UNC (Unified National Coarse) has fewer threads per inch and is more resistant to cross-threading — better for assembly in the field and applications with vibration. UNF (Unified National Fine) has more threads per inch providing greater holding strength and finer adjustment — used in precision and high-strength applications.
What screw head is best for outdoor use?
Torx (star drive) screws are generally preferred for outdoor decking and structural applications because the driver bit seats deeper in the recess and is far less prone to cam-out than Phillips. Stainless steel or ACQ-rated coated screws should be used outdoors to resist corrosion.
What is a #8 screw in metric?
A #8 wood screw has a shank diameter of approximately 0.164" which converts to 4.17 mm. The closest metric wood screw equivalent is an M4 (4.0 mm diameter).
How do I know what size screw to use?
The screw length should be approximately three times the thickness of the piece being fastened — two-thirds of the total length should be in the base piece. For gauge choose a size proportionate to the wood thickness — #6 or #8 for 3/4" stock and #10 or #12 for 1.5" material.
What is a tap drill?
A tap drill is the drill bit size used to create the pilot hole before cutting threads with a tap. The tap drill size is slightly smaller than the nominal thread diameter — leaving enough material for the tap to cut threads into.
What is the difference between wood screws and machine screws?
Wood screws have sharp threads designed to cut into wood fibres and a tapered shank that pulls pieces together. Machine screws have uniform threads designed to mate with a tapped hole or nut — they require a pre-drilled clearance hole and cannot self-thread into wood.