Wrench & Socket Size Chart

Wrench & Socket Size Chart

Complete reference for bolt head sizes, wrench sizes, and socket sizes — SAE, Metric, and Structural

Find the right wrench or socket for any hex bolt, nut, or cap screw. This chart covers SAE (inch), Metric, and Structural fasteners with their corresponding wrench sizes.

💡 Quick Tip: Bolt Size ≠ Wrench Size

A "1/2 inch bolt" refers to the thread diameter, not the head size. A 1/2"-13 hex bolt actually requires a 3/4" wrench. The charts below show the correct wrench size for each bolt size.

SAE Hex Bolt & Cap Screw Wrench Sizes

Bolt Diameter Hex Bolt Head Heavy Hex Head Socket Cap (Allen)
#6 (0.138") 5/16" — 7/64"
#8 (0.164") 11/32" — 9/64"
#10 (0.190") 3/8" — 5/32"
1/4" (0.250") 7/16" — 3/16"
5/16" (0.312") 1/2" — 1/4"
3/8" (0.375") 9/16" — 5/16"
7/16" (0.437") 5/8" — 3/8"
1/2" (0.500") 3/4" 7/8" 3/8"
9/16" (0.562") 13/16" 15/16" 7/16"
5/8" (0.625") 15/16" 1-1/16" 1/2"
3/4" (0.750") 1-1/8" 1-1/4" 5/8"
7/8" (0.875") 1-5/16" 1-7/16" 3/4"
1" (1.000") 1-1/2" 1-5/8" 3/4"
1-1/8" (1.125") 1-11/16" 1-13/16" 7/8"
1-1/4" (1.250") 1-7/8" 2" 1"

Metric Hex Bolt & Cap Screw Wrench Sizes

Bolt Diameter Hex Bolt Head Socket Cap (Allen) Closest SAE
M3 (3mm) 5.5mm 2.5mm —
M4 (4mm) 7mm 3mm 9/32"
M5 (5mm) 8mm 4mm 5/16"
M6 (6mm) 10mm 5mm 3/8"
M8 (8mm) 13mm 6mm 1/2"
M10 (10mm) 17mm 8mm 11/16"
M12 (12mm) 19mm 10mm 3/4"
M14 (14mm) 22mm 12mm 7/8"
M16 (16mm) 24mm 14mm 15/16"
M18 (18mm) 27mm 14mm 1-1/16"
M20 (20mm) 30mm 17mm 1-3/16"
M24 (24mm) 36mm 19mm 1-7/16"

Structural Bolt Wrench Sizes (A325 / A490 / F3125)

Bolt Diameter Heavy Hex Head Heavy Hex Nut TC Bolt Spline
1/2" 7/8" 7/8" 7/16"
5/8" 1-1/16" 1-1/16" 9/16"
3/4" 1-1/4" 1-1/4" 11/16"
7/8" 1-7/16" 1-7/16" 13/16"
1" 1-5/8" 1-5/8" 15/16"
1-1/8" 1-13/16" 1-13/16" 1-1/16"
1-1/4" 2" 2" 1-3/16"

Hex Nut Wrench Sizes

SAE Hex Nuts

#6 → 5/16"
#8 → 11/32"
#10 → 3/8"
1/4" → 7/16"
5/16" → 1/2"
3/8" → 9/16"
1/2" → 3/4"
5/8" → 15/16"
3/4" → 1-1/8"
1" → 1-1/2"

Metric Hex Nuts

M3 → 5.5mm
M4 → 7mm
M5 → 8mm
M6 → 10mm
M8 → 13mm
M10 → 17mm
M12 → 19mm
M14 → 22mm
M16 → 24mm
M20 → 30mm

SAE ↔ Metric Wrench Conversions

In a pinch, these SAE and metric wrenches are close enough to substitute (within 0.5mm). Bold pairs are nearly exact.

SAE Wrench Metric Wrench Difference
1/4" (6.35mm) 6mm 0.35mm ✓
5/16" (7.94mm) 8mm 0.06mm ✓
3/8" (9.52mm) 10mm 0.48mm
7/16" (11.11mm) 11mm 0.11mm
1/2" (12.70mm) 13mm 0.30mm ✓
9/16" (14.29mm) 14mm 0.29mm
5/8" (15.87mm) 16mm 0.13mm
11/16" (17.46mm) 17mm 0.46mm
3/4" (19.05mm) 19mm 0.05mm ✓
15/16" (23.81mm) 24mm 0.19mm

Frequently Asked Questions

Why is the wrench size different from the bolt size?
The bolt size (1/4", 3/8", 1/2", etc.) refers to the thread diameter — the part that screws into the hole. The wrench size is the distance across the flats of the hex head, which must be larger than the thread to provide enough material strength. A general rule: wrench size ≈ 1.5× bolt diameter.
Can I use a metric wrench on SAE bolts (or vice versa)?
In emergencies, yes — if the sizes are close (see conversion table above). For example, a 13mm wrench works on 1/2" hex heads. However, using the wrong size risks rounding off the bolt head corners. For regular use, always use the correct wrench.
What's the difference between hex bolts and heavy hex bolts?
Heavy hex bolts have a larger head (and require a larger wrench) than standard hex bolts of the same diameter. Heavy hex is standard for structural applications (A325, A490) because the larger head provides more bearing surface and can handle higher torque values.
What size Allen key do I need for socket cap screws?
Socket cap screws use an internal hex (Allen) drive. The key size is typically about 1/2 the bolt diameter for inch sizes (e.g., 1/4" bolt uses 3/16" Allen) and follows a standard progression for metric. See the Socket Cap column in the tables above.
Why do some bolts have the same wrench size but different thread sizes?
Head dimensions are standardized by grade and application, not just thread size. For example, heavy hex heads on 1/2" and 9/16" structural bolts might both use a 7/8" wrench. This is why it's important to know the bolt specification, not just match wrenches by feel.

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