Wrench size chart for bolts and nuts.
The wrench or socket for every hex and heavy hex bolt, cap screw and nut from 1/4 to 4 in., and for metric bolts and nuts from M5 to M64, taken from the width across flats in the ASME, ISO and DIN standards.
| Bolt or nut size (in.) | Hex | Heavy hex | ||
|---|---|---|---|---|
| Bolt / cap screw | Nut | Bolt / screw | Nut | |
| 1/4" | 7/16 | 7/16 | — | 1/2 |
| 5/16" | 1/2 | 1/2 | — | 9/16 |
| 3/8" | 9/16 | 9/16 | 11/16 | 11/16 |
| 7/16" | 5/8 | 11/16 | — | 3/4 |
| 1/2" | 3/4 | 3/4 | 7/8 | 7/8 |
| 9/16" | 13/16 | 7/8 | — | 15/16 |
| 5/8" | 15/16 | 15/16 | 1-1/16 | 1-1/16 |
| 3/4" | 1-1/8 | 1-1/8 | 1-1/4 | 1-1/4 |
| 7/8" | 1-5/16 | 1-5/16 | 1-7/16 | 1-7/16 |
| 1" | 1-1/2 | 1-1/2 | 1-5/8 | 1-5/8 |
| 1-1/8" | 1-11/16 | 1-11/16 | 1-13/16 | 1-13/16 |
| 1-1/4" | 1-7/8 | 1-7/8 | 2 | 2 |
| 1-3/8" | 2-1/16 | 2-1/16 | 2-3/16 | 2-3/16 |
| 1-1/2" | 2-1/4 | 2-1/4 | 2-3/8 | 2-3/8 |
| 1-5/8" | 2-7/16 | see note | 2-9/16 | 2-9/16 |
| 1-3/4" | 2-5/8 | 2-5/8 | 2-3/4 | 2-3/4 |
| 1-7/8" | 2-13/16 | 2-13/16 | 2-15/16 | 2-15/16 |
| 2" | 3 | 3 | 3-1/8 | 3-1/8 |
| 2-1/4" | 3-3/8 | 3-3/8 | 3-1/2 | 3-1/2 |
| 2-1/2" | 3-3/4 | 3-3/4 | 3-7/8 | 3-7/8 |
| 2-3/4" | 4-1/8 | 4-1/8 | 4-1/4 | 4-1/4 |
| 3" | 4-1/2 | 4-1/2 | 4-5/8 | 4-5/8 |
| 3-1/4" | 4-7/8 | 4-7/8 | 5 | 5 |
| 3-1/2" | 5-1/4 | 5-1/4 | 5-3/8 | 5-3/8 |
| 3-3/4" | 5-5/8 | 5-5/8 | 5-3/4 | 5-3/4 |
| 4" | 6 | 6 | 6-1/8 | 6-1/8 |
Wrench sizes in inches: the basic width across flats. Hex bolts and hex cap screws share a head width, as do heavy hex bolts and heavy hex screws. — = not made in that pattern. The standard prints 2.430 - 2.350 in. across the flats for the 1-5/8 hex nut, which is not a fractional wrench size.
| Size | Pitch (mm) | ISO | DIN | ||
|---|---|---|---|---|---|
| Bolt (ISO 4014) | Nut (ISO 4032) | Bolt (DIN 931) | Nut (DIN 934) | ||
| M5 | 0.8 | 8 | 8 | 8 | 8 |
| M6 | 1 | 10 | 10 | 10 | 10 |
| M8 | 1.25 | 13 | 13 | 13 | 13 |
| M10 | 1.5 | 16 | 16 | 17 | 17 |
| M12 | 1.75 | 18 | 18 | 19 | 19 |
| M14 | 2 | 21 | 21 | 22 | 22 |
| M16 | 2 | 24 | 24 | 24 | 24 |
| M18 | 2.5 | 27 | 27 | 27 | 27 |
| M20 | 2.5 | 30 | 30 | 30 | 30 |
| M22 | 2.5 | 34 | 34 | 32 | 32 |
| M24 | 3 | 36 | 36 | 36 | 36 |
| M27 | 3 | 41 | 41 | 41 | 41 |
| M30 | 3.5 | 46 | 46 | 46 | 46 |
| M33 | 3.5 | 50 | 50 | 50 | 50 |
| M36 | 4 | 55 | 55 | 55 | 55 |
| M39 | 4 | 60 | 60 | 60 | 60 |
| M42 | 4.5 | 65 | 65 | 65 | 65 |
| M45 | 4.5 | 70 | 70 | 70 | 70 |
| M48 | 5 | 75 | 75 | 75 | 75 |
| M52 | 5 | 80 | 80 | 80 | 80 |
| M56 | 5.5 | 85 | 85 | 85 | 85 |
| M60 | 5.5 | 90 | 90 | 90 | 90 |
| M64 | 6 | 95 | 95 | 95 | 95 |
Wrench sizes in mm: the nominal width across flats s. ISO and DIN differ at M10, M12, M14 and M22.
Dimensions from ASME B18.2.1-2012 and ASME B18.2.2-2015 as printed in the IFI Book of Fastener Standards (2018) and cross-checked against the IFI Technology Connection; metric from ISO 4014:2011, ISO 4032:2012, DIN 931 and DIN 934. Full head and nut dimensions are on the bolt size chart and the heavy hex nut chart.
Wrench sizes: common questions.
What size wrench for a 1/2 inch bolt?
3/4 in. for a 1/2 in. hex bolt, hex cap screw or hex nut, and 7/8 in. for a 1/2 in. heavy hex bolt or heavy hex nut.
What size wrench for a 3/4 inch bolt?
1-1/8 in. for a hex bolt or hex nut, and 1-1/4 in. for a heavy hex bolt or heavy hex nut.
What size wrench for a 1 inch bolt?
1-1/2 in. for a hex bolt or hex nut, and 1-5/8 in. for a heavy hex bolt or heavy hex nut, per ASME B18.2.1 and B18.2.2.
Does a bolt always take the same wrench as its nut?
Not always. At 7/16 in. a hex bolt takes 5/8 in. but a hex nut takes 11/16 in., and heavy hex nuts come in sizes (1/4, 5/16, 7/16, 9/16 in.) that heavy hex bolts do not. The table gives each separately.
What size wrench for M10, M12 and M16 bolts?
ISO 4014 bolts and ISO 4032 nuts: M10 16 mm, M12 18 mm, M16 24 mm. Older DIN 931 and DIN 934 parts are 17 mm at M10 and 19 mm at M12; M16 is 24 mm in both.
Engineering tools from our shop.
Bolt torque calculator
Preload and tightening torque from size, grade, nut factor K and target % of yield or proof load, inch and metric.
Bolt size chart
Hex and heavy hex bolt and cap screw head dimensions: across flats, across corners, head height. ASME B18.2.1 and ISO 4014.
Heavy hex nut chart
Heavy hex, hex and jam nut dimensions: width across flats and corners, thickness. ASME B18.2.2 and ISO 4032.