The professional workshop standard for matching wrenches to fasteners. Compare Metric (mm) and SAE (Inch) sizes for Hex bolts, Heavy Hex, and Socket Cap screws. Includes the critical ISO vs DIN head size differences.
Auto Mechanic • Metric & SAE • all
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Metric & SAE Wrench Comparison • A4
| Wrench Size | Actual (mm) | Metric Hex | SAE Hex | Metric Socket | SAE Socket | Heavy Hex |
|---|---|---|---|---|---|---|
| 0.050" | 1.27 | - | - | - | #3, #4 | - |
| 1.5mm | 1.50 | - | - | M1.6, M2 | - | - |
| 1/16" | 1.59 | - | - | - | #5, #6 | - |
| 5/64" | 1.98 | - | - | - | #8 | - |
| 2mm | 2.00 | - | - | M2.5 | - | - |
| 3/32" | 2.38 | - | - | - | #10, 1/8" | - |
| 2.5mm | 2.50 | - | - | M3 | - | - |
| 7/64" | 2.78 | - | - | - | #6 | - |
| 3mm | 3.00 | - | - | M4 | - | - |
| 9/64" | 3.57 | - | - | - | #8 | - |
| 5/32" | 3.97 | - | #6 (Small Pattern) | - | #10 | - |
| 4mm | 4.00 | - | - | M5 | - | - |
| 3/16" | 4.76 | - | #8 (Small Pattern) | - | 1/4" | - |
| 5mm | 5.00 | - | - | M6 | - | - |
| 5.5mm | 5.50 | M3 | - | - | - | - |
| 6mm | 6.00 | - | - | M8 | - | - |
| 1/4" | 6.35 | - | #6 | - | 5/16" | - |
| 7mm | 7.00 | M4 | - | - | - | - |
| 5/16" | 7.94 | - | #8, #10 | - | 3/8" | - |
| 8mm | 8.00 | M5 | - | M10 | - | - |
| 11/32" | 8.73 | - | #8 (Heavy), #10 (Small) | - | - | - |
| 3/8" | 9.52 | - | #10 (Heavy), 1/4" (Small) | - | 7/16", 1/2" | - |
| 10mm | 10.00 | M6 | - | M12 | - | - |
| 7/16" | 11.11 | - | 1/4" | - | - | - |
| 12mm | 12.00 | - | - | M14 | - | - |
| 1/2" | 12.70 | - | 5/16" | - | 5/8" | - |
| 13mm | 13.00 | M8 | - | - | - | - |
| 14mm | 14.00 | - | - | M16 | - | - |
| 9/16" | 14.29 | - | 3/8" | - | - | - |
| 5/8" | 15.88 | - | 7/16" | - | 3/4" | - |
| 16mm | 16.00 | M10 (ISO) | - | - | - | - |
| 17mm | 17.00 | M10 (DIN) | - | M20 | - | - |
| 18mm | 18.00 | M12 (ISO) | - | - | - | - |
| 19mm | 19.00 | M12 (DIN) | - | M24 | - | - |
| 3/4" | 19.05 | - | 1/2" | - | 7/8", 1" | - |
| 13/16" | 20.64 | - | 9/16" | - | - | - |
| 21mm | 21.00 | M14 (ISO) | - | - | - | - |
| 22mm | 22.00 | M14 (DIN) | - | - | - | - |
| 7/8" | 22.22 | - | - | - | - | 1/2" (Heavy) |
| 15/16" | 23.81 | - | 5/8" | - | - | - |
| 24mm | 24.00 | M16 | - | - | - | - |
| 27mm | 27.00 | M18 | - | - | - | - |
| 30mm | 30.00 | M20 | - | - | - | - |
| 32mm | 32.00 | M22 (DIN) | - | - | - | - |
| 34mm | 34.00 | M22 | - | - | - | - |
| 36mm | 36.00 | M24 | - | - | - | - |
| 1-1/8" | NaN | - | 3/4" | - | - | - |
| 1-5/16" | NaN | - | 7/8" | - | - | - |
| 1-1/2" | NaN | - | 1" | - | - | - |
| 1-1/16" | NaN | - | - | - | - | 5/8" (Heavy) |
| 1-1/4" | NaN | - | - | - | - | 3/4" (Heavy) |
| 1-7/16" | NaN | - | - | - | - | 7/8" (Heavy) |
| 1-5/8" | NaN | - | - | - | - | 1" (Heavy) |
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Metric & SAE • all
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Can you substitute? While some sizes are nearly identical, using the wrong system is the #1 cause of rounded-off bolt heads.
The "Emergency" Matches:
Note: 13mm is slightly larger than 1/2". Use a 13mm wrench on a 1/2" bolt only in low-torque situations.
For stubborn or rusted bolts, always use a 6-point socket or wrench. 12-point tools are easier to align in tight spaces but only grip the corners of the bolt, making them much more likely to slip and "round off" the fastener.
Why does your 17mm wrench fit some M10 bolts but not others? It depends on the engineering standard used.
Stop stripping fasteners! Follow these steps to ensure a perfect tool-to-bolt match.
Use calipers to measure the distance between the two parallel flat sides of the bolt head. This is the wrench size.
Look for markings. Numbers (8.8, 10.9) mean Metric tools. Hash marks or letters mean SAE (Inch) tools.
Ensure the wrench has zero 'play'. If the wrench can wiggle on the bolt, it is the wrong size or system.
Different bolts require different driving tools. Know when to use each.
Standard combination wrenches are ideal for most tasks. Socket sets are preferred for engine bays where space is limited.
Precision equipment often uses Heavy Hex or Socket Cap bolts that require heavy-duty impact sockets or Hex keys.
Flat-pack furniture (IKEA style) relies heavily on metric Hex keys. Keep a set of 4mm, 5mm, and 6mm handy.
Complete your garage reference wall with these printable guides.
| Size | Pitch/TPI | Head |
|---|---|---|
| M3 | 0.5 | 5.5 |
| M4 | 0.7 | 7.0 |
| M5 | 0.8 | 8.0 |
| M6 | 1.0 | 10.0 |
| M8 | 1.25 | 13.0 |
| 1/4" | 20 | 7/16" |
| 5/16" | 18 | 1/2" |
| 3/8" | 16 | 9/16" |
| Number | Fraction | Decimal (in) | Millimeters |
|---|---|---|---|
| #80 | — | 0.0135 | 0.34 |
| #50 | — | 0.0700 | 1.78 |
| #52 | 1/16" | 0.0625 | 1.59 |
| #41 | 3/32" | 0.0938 | 2.38 |
| #22 | 5/32" | 0.1562 | 3.97 |
| #11 | 3/16" | 0.1875 | 4.76 |
| #7 | 13/64" | 0.2031 | 5.16 |
| — | — | 0.2570 | 6.53 |
| — | 3/8" | 0.3750 | 9.53 |
| — | 1/2" | 0.5000 | 12.70 |
| Size | Pilot | Clear |
|---|---|---|
| #4 | 1/16" | 9/64" |
| #6 | 5/64" | 11/64" |
| #8 | 3/32" | 13/64" |
| #10 | 7/64" | 1/4" |
| #12 | 1/8" | 17/64" |
| 1/4" | - | F |
| 5/16" | - | P |
| 3/8" | - | W |
| M4 | 2.5mm | 4.5mm |
| M6 | 3.5mm | 6.6mm |
Identify screw sizes, thread pitches, and head types for woodworking and repairs.
Customize & Download| Nominal | Actual Size |
|---|---|
| 1 x 2 | 3/4" x 1 1/2" |
| 1 x 3 | 3/4" x 2 1/2" |
| 1 x 4 | 3/4" x 3 1/2" |
| 2 x 4 | 1 1/2" x 3 1/2" |
| 2 x 6 | 1 1/2" x 5 1/2" |
| 2 x 8 | 1 1/2" x 7 1/4" |
| 4 x 4 | 3 1/2" x 3 1/2" |
| 4/4 | 13/16" |
| 8/4 | 1 3/4" |
| 3/4" Ply | 23/32" |
Nominal vs actual lumber sizes for woodworking and construction planning.
Customize & Download