M12 bolt ke liye kaunsa spanner?

M12 standard hex bolt ke liye 19 mm spanner. M12 Unbrako socket head cap screw ke liye 10 mm allen key. Thin head M12 variants 18 mm spanner le sakte hain.

1/2 inch = 12.70 mm exactly. A 13 mm metric spanner works with 0.3 mm slack (acceptable), but a 12 mm will not fit.

Can I use an imperial wrench on a metric bolt (or vice versa)?

Only if the size match is within 0.5 mm. A 1/2 AF spanner on a 13 mm metric bolt works (0.3 mm slack). A 9/16 AF on a 14 mm metric bolt works (0.29 mm slack). Beyond 0.5 mm slack you risk rounding off the bolt head — always use the correct system when possible.

Why are some M10 bolts 16 mm and others 17 mm?

ISO 4014 standard M10 hex bolt has 16 mm AF (often called 'thin head') for reduced material. Older DIN 931 standard has 17 mm AF. Both are valid — check the actual bolt head before fitting a spanner.

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Wrench / Spanner Size Converter (AF ↔ Metric)

Convert imperial AF wrench sizes to metric and vice versa

AF (इंच) स्पैनर को मिमी में बदलें — और बोल्ट साइज़ से स्पैनर चुनें

Quick Overview

Wrench (spanner) sizes are measured across the flats — the distance between two opposite sides of the hex head. Imperial wrenches are stamped in fractions of an inch (1/4, 3/8, 1/2, 9/16), while metric wrenches are in whole mm (10, 13, 17, 19). Conversion is simple multiplication by 25.4: 1/2 inch = 12.7 mm (a 13 mm metric wrench fits), 9/16 = 14.29 mm (14 mm metric fits), 3/4 = 19.05 mm (19 mm metric fits). For a metric hex bolt, the wrench size is standardised: M6 needs a 10 mm spanner, M8 needs 13 mm, M10 needs 17 mm (standard head) or 16 mm (thin head), M12 needs 19 mm, M16 needs 24 mm. This converter does both: imperial↔metric conversion and direct bolt→wrench lookup. Essential when working on mixed US / Indian equipment in a workshop.

Calculator

Convert from(कौनसा input)

Imperial AF size (inch)

Imperial AF

1/2"

Equals

12.70mm

Metric wrench

13mm

13 mm metric wrench fits (slack 0.30 mm — acceptable).

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ƒFormula

AF (mm) = AF (inch) × 25.4 | Metric wrench fits imperial if (metric − imperial×25.4) < 0.5

Imperial-to-metric conversion is exact mathematically. In practice, a metric wrench within 0.5 mm of the imperial size works with slight slack. Go tighter (metric smaller than imperial) and it won't fit. Go looser (more than 0.5 mm) and it'll round off the bolt corners.

Units: Across flats (AF): inch (imperial) or millimetre (metric)

Spanner size kaise decide karein?

Spanner (wrench) ki size bolt ke head ke 'across flats' (AF) measurement hoti hai, yaani do opposite flat sides ke beech ki distance. Imperial spanners inches mein hote hain (1/4, 3/8, 1/2 AF), metric mm mein (10, 13, 17, 19 mm). Inches ko mm mein convert karne ka formula: AF(mm) = AF(inch) × 25.4. Direct rule of thumb Indian workshop mein: M8 bolt → 13 mm spanner, M10 → 17 mm, M12 → 19 mm, M16 → 24 mm. Kabhi-kabhi 'thin head' bolts pe size different hoti hai, M10 thin head ke liye 16 mm spanner use hota hai.

उदाहरण / Example: Example: Imported American equipment pe '9/16 AF' bolt hai. Local hardware shop pe sirf metric spanners milte hain. 9/16 × 25.4 = 14.29 mm, toh 14 mm metric spanner fit ho jayega (slight slack).

Worked Examples

Working on an imported machine with only metric tools

Problem: An American CNC machine has 3/4 AF bolts. You only have metric spanners.

Solution: 3/4 inch = 19.05 mm. A 19 mm metric spanner fits (0.05 mm slack, negligible). A 20 mm spanner would be too loose. Use the 19 mm.

Buying a spanner set for a new Unbrako workshop

Problem: You need to tighten M6, M8, M10, M12, M16 Unbrako cap screws. Which metric spanner set?

Solution: Note: Unbrako cap screws use allen keys, not spanners. But for standard hex M-bolts: M6 → 10 mm, M8 → 13 mm, M10 → 17 mm, M12 → 19 mm, M16 → 24 mm. A 8-24 mm Venus combination spanner set covers all of these.

Rounded bolt heads from using the wrong size

Problem: A 14 mm spanner on a 9/16 AF bolt rounded the corners. Why?

Solution: 14 mm = 0.551 inch; 9/16 = 0.5625 inch = 14.29 mm. The 14 mm spanner is 0.29 mm too small — it can't fully grip. It bites on two corners and rounds them. Use a 14 mm thin-wall spanner ONLY if tight; otherwise use the correct 9/16 AF.

Wrench Size Chart, AF ↔ Metric ↔ Bolt Size (Standard Hex Head)

AF (inch)	AF (mm)	Metric Wrench	Bolt Size
3/16	4.76	5 mm	M3
1/4	6.35	6 mm	—
9/32	7.14	7 mm	M4
5/16	7.94	8 mm	M5
3/8	9.53	10 mm	M6
7/16	11.11	11 mm	—
1/2	12.70	13 mm	M8
9/16	14.29	14 mm	—
—	—	16 mm	M10 (thin)
11/16	17.46	17 mm	M10
3/4	19.05	19 mm	M12
13/16	20.64	21 mm	—
7/8	22.23	22 mm	M14
15/16	23.81	24 mm	M16
1	25.40	26 mm	—
1-1/16	26.99	27 mm	M18
1-1/8	28.58	29 mm	—
1-3/16	30.16	30 mm	M20
1-1/4	31.75	32 mm	M22
1-7/16	36.51	36 mm	M24

'Thin head' variants of M10 use 16 mm AF instead of 17 mm; check the actual head before assuming. Unbrako socket head cap screws use allen keys, not open-end wrenches.

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Venus Hand Tools

Combination spanners, open-end sets, ring spanners, and socket sets — 6-32 mm metric and imperial AF.

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Frequently Asked Questions: Wrench / Spanner Size Converter (AF ↔ Metric)

Standard hex M10 bolt takes a 17 mm spanner. Thin-head variants take 16 mm. For Unbrako socket head cap screws of size M10, you need a 8 mm allen key instead.

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