---
title: "M20 Thin Hex Nut Dimensions"
description: "M20 Thin Hex Nut: width across flats (spanner size) 30 mm, nut height 10 mm, coarse thread pitch 2.5 mm. Tightening torque 420 Nm at class 8.8."
url: https://engineeringhardware.com/guide/size/m20-cad-svg-055-hexnut/
source: Engineering Hardware & Fasteners
---

# M20 Thin Hex Nut Dimensions

Nuts · GB/T 6172.1 / ISO 4035

Controlling dimensions to GB/T 6172.1 / ISO 4035, with spanner or drive size and tightening torque.

M20 Thin Hex Nut dimensions to GB/T 6172.1 / ISO 4035: width across flats (spanner size) 30 mm, nut height 10 mm, coarse thread pitch 2.5 mm. Tighten to approximately 420 Nm at property class 8.8 in a dry, as-supplied condition.

- **Width across flats (spanner size):** 30 mm
- **Nut height:** 10 mm
- **Coarse thread pitch:** 2.5 mm
- **Tightening torque (class 8.8):** 420 Nm

Figures are nominal values from the governing standard. Confirm against the tolerance class for your application before machining or ordering.

![M20 Thin Hex Nut Dimensions reference image](https://engineeringhardware.com/wp-content/uploads/2026/06/Thin-Hex-Nuts-—-ISO-4035-Detail.webp)

M20 Thin Hex Nut are manufactured to GB/T 6172.1 / ISO 4035. This page lists the controlling dimensions for the M20 size together with the drive and the installation notes for this type.

Values are taken from the governing standard rather than from a general machine-thread table, because this type is not selected on one.

## M20 Dimensional Row (GB/T 6172.1 / ISO 4035)

| Size | Pitch (mm) | Width across flats s (mm) | Width across corners e (mm) | Nut height m (mm) | Reference standard |
| --- | --- | --- | --- | --- | --- |
| M20 | 2.5 | 30.0 | 33.53 | 10.0 | ISO 4035 / GB/T 6172 |

## Spanner & Drive for M20 Thin Hex Nut — GB/T 6172.1 / ISO 4035 (Series 055)

M20 Thin Hex Nut — GB/T 6172.1 / ISO 4035 (Series 055) have a width across flats of 30.0 mm — fit a 30.0 mm open-ended spanner or socket. In tight access a 6-point socket on the 30.0 mm flats gives the most engagement per degree of swing. Where the joint is torqued to a figure, a click wrench is the only way to reproduce it across a batch.

## Tightening Torque for M20

| Class 8.8 (dry, ~µ 0.125) | ≈ 420 Nm |
| --- | --- |
| Class 10.9 (dry, ~µ 0.125) | ≈ 598 Nm |
| Class 12.9 (dry, ~µ 0.125) | ≈ 700 Nm |

Indicative dry-joint values. Lubrication can lower the required torque by 15–25%. Always confirm against the joint design, especially when going up a strength class.

## Proof Load & Strength for M20

Nuts are graded to ISO 898-2 by the proof load the nut itself will hold (classes 04, 05, 5, 6, 8, 10 and 12), not by the 8.8 / 10.9 / 12.9 scale used for bolts. A class-8 nut is the correct mate for a class-8.8 bolt, and the joint is designed on the bolt, so no bolt-tension figure is quoted here.

## Mating Parts for M20

Pair M20 with the matching M20 bolt or screw, plus a M20 flat washer where required to distribute load on softer materials.

## When to Step Up or Down from M20

When the joint preload approaches the proof load of M20 class 8.8, step up to M24 class 8.8 (or move to M20 class 10.9). When the joint is over-specified, M16 often saves weight and cost without losing the safety margin.

Custom manufacturing · Made to drawing

## Need thin hex nut in a size this table does not list?

This page covers M20 thin hex nut. Thread size is the obvious variable and rarely the interesting one — height for clearance, across-flats for the tool already in the cell, and the locking feature for the vibration actually present. Made by cold heading or tapping.

Minimum order from 2,000 pieces; samples within 7 days of drawing approval.

[Custom nut manufacturing](https://engineeringhardware.com/custom/nuts/)[Send a drawing](https://engineeringhardware.com/custom/nuts/#rfq)

## Technical Drawing

Dimensioned line drawing of M20 Thin Hex Nut — GB/T 6172.1 / ISO 4035 (Series 055) to GB/T 6172.1 / ISO 4035. Side view and top view, drawn to the dimensions in the table below and redrawn for any size selected.

- **Pitch (mm):** 2.5
- **Width across flats s (mm):** 30.0
- **Width across corners e (mm):** 33.53
- **Nut height m (mm):** 10.0

## Dimensions & Specifications (GB/T 6172.1 / ISO 4035)

| Size | Pitch (mm) | Width across flats s (mm) | Width across corners e (mm) | Nut height m (mm) | Reference standard |
| --- | --- | --- | --- | --- | --- |
| M3 | 0.5 | 5.5 | 6.01 | 1.8 | ISO 4035 / GB/T 6172 |
| M4 | 0.7 | 7.0 | 7.66 | 2.2 | ISO 4035 / GB/T 6172 |
| M5 | 0.8 | 8.0 | 8.79 | 2.7 | ISO 4035 / GB/T 6172 |
| M6 | 1.0 | 10.0 | 11.05 | 3.2 | ISO 4035 / GB/T 6172 |
| M8 | 1.25 | 13.0 | 14.38 | 4.0 | ISO 4035 / GB/T 6172 |
| M10 | 1.5 | 16.0 | 17.77 | 5.0 | ISO 4035 / GB/T 6172 |
| M12 | 1.75 | 18.0 | 20.03 | 6.0 | ISO 4035 / GB/T 6172 |
| M14 | 2.0 | 21.0 | 23.36 | 7.0 | ISO 4035 / GB/T 6172 |
| M16 | 2.0 | 24.0 | 26.75 | 8.0 | ISO 4035 / GB/T 6172 |
| M18 | 2.5 | 27.0 | 30.14 | 9.0 | ISO 4035 / GB/T 6172 |
| M20 | 2.5 | 30.0 | 33.53 | 10.0 | ISO 4035 / GB/T 6172 |
| M24 | 3.0 | 36.0 | 39.98 | 12.0 | ISO 4035 / GB/T 6172 |
| M30 | 3.5 | 46.0 | 50.85 | 15.0 | ISO 4035 / GB/T 6172 |
| M36 | 4.0 | 55.0 | 60.79 | 18.0 | ISO 4035 / GB/T 6172 |

## Materials & Grades

Select a material class to see the grades we supply it in. Each designation is listed with its ISO/EN, AISI/SAE, JIS and GB equivalents.

Stainless Steel38 Carbon Steel66 Alloy Steel41 Bearing Steel5 Spring Steel25 Aluminum and Aluminum Alloys21 Brass17 Bronze11 Copper8 Titanium and Titanium Alloys18 Nickel and Nickel Alloys22 Iron-Nickel and High-Temperature Alloys10 Tool Steel and Specialty Hardened Steel9 Structural and Construction Steel9

### Stainless Steel

#### Austenitic Stainless Steel

- A1 AISI 303 · SAE 303 · SUS303 · EN 1.4305 · X8CrNiS18-9
- A2 AISI 304 · SAE 304 · SUS304 · EN 1.4301 · X5CrNi18-10 · 06Cr19Ni10
- 304L AISI 304L · SUS304L · EN 1.4307 · X2CrNi18-9 · 022Cr19Ni10
- 302 AISI 302 · SUS302 · EN 1.4310
- 305 AISI 305 · SUS305 · EN 1.4303
- A4 AISI 316 · SAE 316 · SUS316 · EN 1.4401 · X5CrNiMo17-12-2 · 06Cr17Ni12Mo2
- 316L AISI 316L · SUS316L · EN 1.4404 · X2CrNiMo17-12-2 · 022Cr17Ni12Mo2
- 321 AISI 321 · SUS321 · EN 1.4541 · X6CrNiTi18-10
- 310 / 310S AISI 310 · AISI 310S · SUS310S · EN 1.4845
- 302HQ AISI 302HQ
- A3
- A5
- 347 AISI 347 · SUS347 · EN 1.4550 · X6CrNiNb18-10
- 309 / 309S AISI 309 · AISI 309S · SUS309S

#### Martensitic Stainless Steel

- AISI 410 SUS410 · EN 1.4006 · X12Cr13 · 12Cr13
- AISI 420 SUS420J1 · SUS420J2 · EN 1.4021 · EN 1.4028 · 20Cr13 · 30Cr13
- AISI 431 SUS431 · EN 1.4057 · X17CrNi16-2
- C1
- C3
- C4
- AISI 440A
- AISI 440B
- AISI 440C SUS440C · EN 1.4125

#### Ferritic Stainless Steel

- AISI 430 SUS430 · EN 1.4016 · X6Cr17 · 10Cr17
- F1
- AISI 434
- AISI 444

#### Precipitation-Hardening Stainless Steel

- 17-4 PH AISI 630 · UNS S17400 · SUS630 · EN 1.4542 · X5CrNiCuNb16-4
- 15-5 PH UNS S15500
- 17-7 PH UNS S17700

#### Duplex and Super Duplex Stainless Steel

- Duplex 2205 UNS S31803 · UNS S32205 · EN 1.4462
- Super Duplex 2507 UNS S32750 · EN 1.4410
- D2
- D4
- D6
- D8
- Lean Duplex 2101 UNS S32101
- Super Duplex S32760 UNS S32760 · EN 1.4501

### Carbon Steel

#### Low-Carbon Steel

- SAE 1006
- SAE 1008
- SAE 1010
- SAE 1018
- SAE 1020
- Q195
- Q235
- SAE 1012
- SAE 1015
- Q215
- ML08
- ML08Al
- ML10
- ML15
- ML20
- SWRCH6A
- SWRCH8A
- SWRCH10A
- SWRCH12A
- SWRCH15A
- SWRCH18A

#### Medium-Carbon Steel

- SAE 1035
- SAE 1045
- S45C
- C45
- SAE 1030
- SAE 1040
- SAE 1050
- 30
- 35
- 40
- 45
- 50
- S35C
- S40C
- S50C
- C35
- C40

#### High-Carbon Steel

- SAE 1060
- SAE 1070
- 65Mn
- SAE 1065
- SAE 1075
- SAE 1080
- SAE 1085
- SAE 1090
- SAE 1095
- 60
- 65
- 70
- 75
- 80
- 85

#### Cold-Heading Steel

- SWRCH22A
- 10B21
- SWRCH22K
- SWRCH25K
- SWRCH30K
- SWRCH35K
- SWRCH40K
- ML20Mn
- ML25
- ML30
- ML35
- ML40
- 15B25

### Alloy Steel

#### Chromium Steel

- 40Cr
- 45Cr
- AISI 5140
- SAE 5140
- AISI 5120
- SAE 5120
- SCr420
- SCr440

#### Chromium-Molybdenum Steel

- 35CrMo
- 42CrMo
- AISI 4140
- SCM435
- SCM440
- 42CrMo4
- 30CrMo
- AISI 4130
- SAE 4130
- SAE 4140
- AISI 4142
- AISI 4145
- SCM415
- SCM420
- SCM445
- EN 1.7220
- EN 1.7225
- 25CrMo4
- 34CrMo4

#### Nickel-Chromium-Molybdenum Steel

- AISI 4340
- SAE 4340
- 40CrNiMo
- SNCM439
- EN 1.6511
- 36CrNiMo4

#### Boron Alloy Steel

- 10B22
- 10B21
- 15B21
- 15B25
- 20MnTiB
- 20Mn2B
- 35VB
- 40MnB

### Bearing Steel

#### Bearing Steel

- GCr15
- AISI 52100 SAE 52100 · UNS G52986
- SUJ2
- 100Cr6 EN 1.3505
- GCr15SiMn

### Spring Steel

#### Carbon Spring Steel

- SAE 1065
- SAE 1070
- SAE 1075
- SAE 1080
- SAE 1095
- 65
- 70
- 75
- 80
- 65Mn

#### Silicon-Manganese Spring Steel

- 60Si2Mn
- 60Si2MnA
- SUP6
- SUP7

#### Chromium-Vanadium Spring Steel

- 50CrVA
- SAE 6150
- AISI 6150
- SUP10

#### Stainless Spring Steel

- AISI 301
- SUS301
- EN 1.4310
- AISI 302
- AISI 304
- AISI 316
- 17-7 PH

### Aluminum and Aluminum Alloys

#### Commercially Pure Aluminum

- 1050
- 1060
- 1070
- 1100

#### 2xxx Series Aluminum

- 2024
- 2011
- 2014
- 2017

#### 5xxx Series Aluminum

- 5052
- 5083
- 5754

#### 6xxx Series Aluminum

- 6061
- 6061-T6
- 6063
- 6082
- 6082-T6

#### 7xxx Series Aluminum

- 7075
- 7075-T6
- 7005
- 7050
- 7075-T73

### Brass

#### Free-Cutting Brass

- C36000
- H62
- HPb59-1
- C3601
- C3602
- C3604
- CuZn36Pb3
- CuZn39Pb3
- EN CW614N
- EN CW617N
- H65

#### Lead-Free Brass

- C69300
- C27450
- CW510L
- CW511L

#### Naval Brass

- C46400
- CuZn39Sn1

### Bronze

#### Silicon Bronze

- C65500
- C65100
- C65600

#### Phosphor Bronze

- C51000
- C52100
- CuSn6
- CuSn8

#### Aluminum Bronze

- C95400
- C95500
- C63000
- CuAl10Ni5Fe4

### Copper

#### Copper

- C11000
- T2
- C10100
- C10200
- C12200
- T1
- TU1
- TU2

### Titanium and Titanium Alloys

#### Commercially Pure Titanium

- Grade 2
- Grade 1
- Grade 3
- Grade 4
- TA1
- TA2
- TA3

#### Alpha-Beta Titanium Alloys

- Grade 5
- Ti-6Al-4V
- TC4
- UNS R56400

#### Low-Interstitial Grade

- Grade 23
- Ti-6Al-4V ELI
- UNS R56407

#### Other Titanium Fastener Alloys

- Ti-6Al-6V-2Sn
- Ti-6Al-2Sn-4Zr-2Mo
- Beta-C titanium
- Ti-10V-2Fe-3Al

### Nickel and Nickel Alloys

#### Commercially Pure Nickel

- Nickel 200
- UNS N02200
- Nickel 201
- UNS N02201

#### Inconel Alloys

- Inconel 625 UNS N06625
- Inconel 718 UNS N07718
- Inconel 600 UNS N06600
- Inconel 601 UNS N06601
- Inconel 686 UNS N06686
- Inconel X-750 UNS N07750

#### Monel Alloys

- Monel 400 UNS N04400
- Monel K-500 UNS N05500

#### Hastelloy Alloys

- Hastelloy C-276 UNS N10276
- Hastelloy C-22 UNS N06022
- Hastelloy B-2 UNS N10665
- Hastelloy B-3 UNS N10675
- Hastelloy X UNS N06002

#### Other Nickel Alloys

- Alloy 20 UNS N08020
- Alloy 625
- Alloy 718
- Alloy 825 UNS N08825
- Alloy 925 UNS N09925

### Iron-Nickel and High-Temperature Alloys

#### A286

- A-286
- UNS S66286
- EN 1.4980

#### Invar

- Invar 36
- Alloy 36
- UNS K93600
- FeNi36

#### Alloy 42

- Alloy 42
- UNS K94100
- FeNi42

### Tool Steel and Specialty Hardened Steel

#### Tool Steel and Specialty Hardened Steel

- AISI D2
- AISI H13
- SKD11
- Cr12MoV
- AISI O1
- AISI A2
- AISI S7
- SKD61
- 9CrSi

### Structural and Construction Steel

#### Structural and Construction Steel

- ASTM A36
- Q235B
- Q355B
- S355JR
- Q235C
- Q355C
- S235JR
- S275JR
- S355J2

## Applications & Industries for M20 Thin Hex Nut

Where Thin Hex Nut are used, and what decides the specification in each case. Stocked from M3 to M36.

### Industries that specify Thin Hex Nut

- **Automotive & transport:** Vibration-prone joints where the locking type is specified on the drawing.
- **Maintenance & MRO:** Replacements matched to the existing bolt class, thread and finish.
- **Building services:** Threaded rod, channel and suspension assemblies.
- **Machine building & OEM:** The clamping counter-face on studs and bolts throughout an assembly.
- **Steel fabrication:** Bolted structural and frame connections.

### Typical applications

- locking an adjustment so it cannot drift
- joints re-torqued at a service interval
- completing a bolted joint on a stud, rod or bolt

### Service conditions to specify against

- **Marine and coastal:** Available in A4 (316) stainless for chloride exposure — coastal structures, pool halls, water treatment and deck hardware, where A2 will eventually pit.
- **High load:** Supplied in ISO 898-1 property classes, so the joint can be designed to a stated proof load and tightened to a calculated torque rather than by feel.
- **Match the class:** A nut below the bolt property class strips before the bolt reaches its own limit — pair class 8 nuts with 8.8 bolts, class 10 with 10.9.

[Full application guide: where Thin Hex Nut are used, how to specify them, and the cases they are wrong for](https://engineeringhardware.com/applications/cad-svg-055-hexnut/)

Inside the plant

## Manufactured in our own plant

This part is cold-formed, threaded, heat-treated and finished in-house. The stages below are where its class and finish are actually decided.

1. ![Wire rod feeding into a cold heading machine](https://engineeringhardware.com/wp-content/uploads/2026/08/09-wire-rod-feed-cold-heading-machine.webp) 01 **Cold heading** Wire rod is drawn to size and cold-formed into blanks. Forming rather than cutting keeps the grain flow continuous around the head, which is where a bolt is most likely to fail. Head dimensions and under-head radius checked at set-up and per shift.
2. ![Thread rolling machine producing bolt threads](https://engineeringhardware.com/wp-content/uploads/2026/08/03-thread-rolling-machine-bolt-production.webp) 02 **Thread rolling** Threads are rolled between hardened dies rather than cut. Rolled threads are stronger in fatigue than cut threads and hold pitch and flank angle far more consistently across a batch. Go / no-go ring gauges to ISO 965 tolerance class 6g.
3. ![Baskets of bolts staged for heat treatment](https://engineeringhardware.com/wp-content/uploads/2026/08/05-heat-treatment-baskets-black-bolts.webp) 03 **Heat treatment** Quench-and-temper brings carbon and alloy steel to the property class ordered — 8.8, 10.9 or 12.9 — with the furnace charge tracked so a finished lot can be traced back to it. Core hardness and tensile tested per lot to ISO 898-1.
4. ![Zinc plated bolts in a treatment basket](https://engineeringhardware.com/wp-content/uploads/2026/08/23-zinc-plated-bolts-treatment-basket.webp) 04 **Surface treatment** Zinc, zinc-nickel, hot-dip galvanizing, black oxide, phosphate and Dacromet, selected against the service environment rather than against the price list. Coating thickness and neutral salt spray hours to ISO 9227.

## Frequently Asked Questions

### What spanner size fits M20 Thin Hex Nut — GB/T 6172.1 / ISO 4035 (Series 055)?

The width across flats for M20 Thin Hex Nut — GB/T 6172.1 / ISO 4035 (Series 055) is 30.0 mm, so a 30.0 mm spanner or 6-point socket fits.

### What is the coarse-thread pitch of M20 for Thin Hex Nut — GB/T 6172.1 / ISO 4035 (Series 055)?

For M20 the standard coarse pitch is 2.5 mm — this is the value used for Thin Hex Nut — GB/T 6172.1 / ISO 4035 (Series 055).

### What clearance and tapping drill suit M20?

Use a 22 mm clearance hole (ISO 273 medium) for through-fixing, or a 17.5 mm tapping drill for a coarse M20 thread.

### Should M20 Thin Hex Nut — GB/T 6172.1 / ISO 4035 (Series 055) be tightened by torque or by angle?

For critical structural joints at M20, angle-controlled or stretch-controlled tightening is more repeatable than pure torque — the friction scatter at large diameters can dominate the torque signal.

### How do I request a quotation?

Use the technical drawing on this page to pick the exact configuration, then submit it with the quote form. We respond within one business day.

## Related Pages

[View the full Thin Hex Nut — GB/T 6172.1 / ISO 4035 (Series 055) page](https://engineeringhardware.com/fastener/cad-svg-055-hexnut/)

### More Thin Hex Nut — GB/T 6172.1 / ISO 4035 (Series 055) Guides