Engineering Tools · Wrench and Socket Openings
Wrench and Socket Opening Chart: M6–M36 Bolt Wrench Sizes
Family index of the wrench and socket opening charts: all 14 sizes from M6 to M36 in one place, giving the width across flats of the hex head bolt, the hex nut, the flange nut and the carriage bolt square neck, plus the nominal wrench or socket opening for the bolt column. Each size opens its own page. Values come from the same engine and size basis as the per-size pages (ISO/GB reduced series), with nothing copied by hand.
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Size Index ({sizes})
Click a size for its own page (four rows side by side, row-level standards, the full-range matrix and the series-difference note). Widths across flats are nominal. This page is ISO/GB throughout: bolts GB/T 5782-2025 / ISO 4014, nuts GB/T 6170-2015 / ISO 4032, flange nuts GB/T 6177.1-2016 type 2, carriage bolt necks GB/T 12-2013. A dash means this chart has no value for that combination and does not interpolate.
| Size | Bolt s (mm) | Wrench / socket (nominal) | Nut s (mm) | Flange nut s (mm) | Carriage bolt neck s (mm) |
|---|---|---|---|---|---|
| M6 | 10 mm | 10 mm (3/8″) | 10 mm | 10 mm | 6.3 mm |
| M8 | 13 mm | 13 mm (1/2″) | 13 mm | 13 mm | 8.36 mm |
| M10 | 16 mm | 16 mm (5/8″) | 16 mm | 15 mm | 10.36 mm |
| M12 | 18 mm | 18 mm (11/16″) | 18 mm | 18 mm | 12.43 mm |
| M14 | 21 mm | 21 mm (13/16″) | 21 mm | — | 14.43 mm |
| M16 | 24 mm | 24 mm (15/16″) | 24 mm | 24 mm | 16.43 mm |
| M18 | 27 mm | 27 mm (1 1/16″) | 27 mm | — | — |
| M20 | 30 mm | 30 mm (1 3/16″) | 30 mm | 30 mm | 20.52 mm |
| M22 | 32 mm | 32 mm (1 1/4″) | 34 mm | — | — |
| M24 | 36 mm | 36 mm (1 7/16″) | 36 mm | — | — |
| M27 | 41 mm | 41 mm (1 5/8″) | 41 mm | — | — |
| M30 | 46 mm | 46 mm (1 13/16″) | 46 mm | — | — |
| M33 | 50 mm | 50 mm (1 15/16″) | 50 mm | — | — |
| M36 | 55 mm | 55 mm (2 3/16″) | 55 mm | — | — |
Basis and Disclosed Assumptions
Where the numbers come from
- Every value is derived at render time from fastenerCalc — the same data source the calculators and the weight charts on this site use. Nothing is copied by hand and nothing is extrapolated.
- The bolt column reads SIZES[].hexHead.s (ISO 4014 / GB/T 5782), the nut column SIZES[].hexNut.s (ISO 4032 / GB/T 6170), the flange nut column FN_DIMS (GB/T 6177.1-2016 type 2, covering 6 sizes) and the carriage bolt neck column CB_DIMS (GB/T 12-2013, covering 7 sizes).
- The wrench/socket column is the bolt width across flats as read, with the nearest 1/16″ imperial fraction in brackets (socketSizeLabel). The fractional part is a nominal label, not an inch-size chart and not an exact conversion (13 mm against 1/2 in = 12.7 mm, a difference of 0.3 mm).
Scope and limits
- The chart answers a tool-selection question: which opening fits this bolt or this nut. It is not an acceptance specification and does not replace a drawing.
- Widths across flats are nominal; real parts vary within tolerance, and the fit also depends on the tool's own tolerance band.
- Combinations shown as a dash have no value in this chart's data and are deliberately not interpolated — ask us for the drawing-level figure.
- No heavy hex column is published: the ISO/GB series this chart is built on has no heavy hex sizes (the ASME B18.2.1 / B18.2.6 heavy series is larger across flats and is not interchangeable with regular hex), so take those values from ASME or the drawing.
- This page is on the ISO/GB reduced series throughout, which differs from the withdrawn German DIN 933 / DIN 934 widened series at M10, M12 and M14 (17 / 19 / 22 mm) — confirm the basis on your drawing before ordering tools or fasteners.
References
- GB/T 5782-2016 Hexagon head bolts (National Public Service Platform for Standards Information, China; the across-flats series used for the bolt column)
- GB/T 6170-2015 Style 1 hexagon nuts (National Public Service Platform for Standards Information, China; across-flats series identical to ISO 4032, used for the nut column)
- GB/T 6177.1-2016 Hexagon nuts with flange, type 2 (National Public Service Platform for Standards Information, China; used for the flange nut column, which covers {flangeCount} sizes in this chart)
- GB/T 12-2013 Round head square neck bolts, carriage bolts (National Public Service Platform for Standards Information, China; used for the square neck column)
- ISO 4014 / ISO 4032 — equivalent ISO series for hexagon head bolts and style 1 hexagon nuts, cited for series reference; no table values are reproduced from them
Need the weight of that bolt?
The weight calculator covers hex head bolts: pick the size and the length and get the unit weight, the batch weight and pieces per tonne — on the same engine and data source as this table.
Open the weight calculatorCite this chart
YAXIIO. Wrench and Socket Opening Chart: M6–M36 Bolt Wrench Sizes. https://www.yaxiio.com/en/tools/wrench-size-chart (accessed 2026-10-29).
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FAQ
Do a bolt and its matching nut take the same wrench?
Mostly, and you can check it row by row above. On the basis used here the only size that splits is M22: the bolt is 32 mm across flats while the nut is 34 mm, so the nut needs one step larger than the bolt. Flange nuts are a separate case again — they can be one step smaller than the plain hex nut of the same size (M10: 15 mm on the ISO 4161 / GB/T 6177.1 type 2 series against 16 mm). Read the row for the part you are actually turning instead of assuming the bolt size carries over.
Some charts say M12 takes a 19 mm wrench; this one says 18 mm. Which is right?
Both are correct for their own basis, because two series are in circulation for the same nominal diameter. This page uses the reduced across-flats series (ISO 4014 / GB/T 5782): M10 16 mm, M12 18 mm, M14 21 mm. The withdrawn German DIN 933 / DIN 934 series is one step larger at exactly those three sizes — 17 / 19 / 22 mm — and that is where the widely repeated line about M12 taking 19 mm comes from. The basis named on your drawing or contract decides which one applies.
Will an imperial socket fit a metric bolt?
Close, but treat it as a fallback rather than a substitute. Only a few nominal sizes sit near each other (13 mm against 1/2 in = 12.7 mm; 19 mm against 3/4 in = 19.05 mm), and even a close pair carries visible play. The fractional label in brackets here is the nearest sixteenth by rounding; it does not mean the two are interchangeable. On a tight or already damaged fastener, or with a worn tool, go to the metric size by name.
Related References
Bolt Weight Calculator
For lengths, materials and batch totals outside these tables; the same engine and data source as the charts.
Bolt Torque Chart
Once the tool is chosen, how hard to tighten: torque range and target preload by property class and friction state.
Hex Bolt Weight Chart
Unit weight and kg per 1,000 pcs across the length series at the same size, useful for comparing steel use and freight.
Hex Head Bolt Product Catalog
Request a quote by size, length, property class and coating.
Disclaimer: this table is engineering reference data for tool selection, ordering and fit checking only; it is not a design basis or an acceptance standard.