M18 Nut Dimensions: Hex & Thin Series

Q: What size wrench or spanner do I need for an M18 nut?

An M18 hex nut typically requires a 27 mm wrench or socket. The standard width across flats (s) for an M18 nut is 27.00 mm. Given the high torque requirements of this size, high-leverage breaker bars or impact wrenches are commonly used for installation.

Q: What is a jam nut?

A jam nut is a low-profile hex nut, typically from the Thin Series (DIN 439), that is used to lock a standard nut in place. By tightening a standard nut against a jam nut, you create internal tension between the threads of both nuts and the bolt. This “jams” the assembly together, providing a mechanical lock that prevents loosening caused by vibration or rotation.

Q: Can a Thin Series nut handle the same torque as a Regular nut?

No. Because the Thin Series has fewer threads in contact with the bolt, it has a lower proof load. For M18 fasteners used in structural or high-stress environments, using a thin nut as the primary fastener could result in thread stripping or joint failure. Always use a standard height nut for primary load-bearing tasks.

Q: Where are M18 nuts most commonly used?

M18 nuts are a “heavy-load” size often found in automotive truck suspensions, large agricultural equipment, and specialized construction machinery where M16 is insufficient but M20 exceeds the required space constraints.

M18 nut dimensions or sizes are critical for heavy equipment manufacturing, transmission towers, and large-scale marine engineering. This size is specifically engineered to mate with fasteners having an 18.00mm nominal diameter and is available in M18 x 2.5 for the coarse series and M18 x 1.5 for the fine series.

This reference guide covers both the Regular Series (DIN 934 / ISO 4032) for standard load-bearing applications and the Thin or Half Series (DIN 439 / ISO 4035), which is ideal for jam nut or lock nut configurations or applications with limited vertical clearance. The thread dimensions comply with DIN 13-1 (coarse), DIN 13-21 (fine series), and ISO 68-1 standards to ensure a precise fit and reliable engagement across heavy-duty metric fastening systems.

Disclaimer: Actual dimensions, including the width across flats (spanner or wrench size), nut height, and thread tolerance may vary depending on the specific manufacturing class and material — always verify with the official product datasheet before use or buying.

Nut internal thread diagram depicting major diameter, minor diameter, and pitch diameter

Nut body diagram depicting width across flats, width across corners, diameter, and thickness or height

M18 x 2.5 Hex Nut – DIN 13-1/ISO 68-1
Dimension	Size (mm)
Dimension	Min	Max
Major Diameter	18	18.585
Pitch Diameter	16.376	16.601
Minor Diameter	15.294	15.744
Thread Pitch	2.5

M18 x 2.0 Hex Nut – DIN 13-21/ISO 68-1
Dimension	Size (mm)
Dimension	Min	Max
Major Diameter	18	18.501
Pitch Diameter	16.701	16.913
Minor Diameter	15.835	16.21
Thread Pitch	2.0

M18 x 1.5 Hex Nut – DIN 13-21/ISO 68-1
Dimension	Size (mm)
Dimension	Min	Max
Major Diameter	18	18.406
Pitch Diameter	17.026	17.216
Minor Diameter	16.376	16.676
Thread Pitch	1.5

M18 x 1.0 Hex Nut – DIN 13-21/ISO 68-1
Dimension	Size (mm)
Dimension	Min	Max
Major Diameter	18	18.304
Pitch Diameter	17.35	17.51
Minor Diameter	16.917	17.153
Thread Pitch	1.0

M18 Hex Nut – DIN 934/ISO 4032 & ISO 8673
Diameter	18	19.5
Width Across Flats	26.16	27
Width Across Corners	29.56	Not specified
Height / Thickness	15.1	15.8

M18 Thin / Half Nut – DIN 439/ISO 4035 & ISO 8675
Diameter	18	19.5
Width Across Flats	26.16	27
Width Across Corners	29.56	Not specified
Height / Thickness	8.42	9

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Frequently Asked Questions

What size wrench or spanner do I need for an M18 nut?

An M18 hex nut typically requires a 27 mm wrench or socket. The standard width across flats (s) for an M18 nut is 27.00 mm. Given the high torque requirements of this size, high-leverage breaker bars or impact wrenches are commonly used for installation.

What is a jam nut?

A jam nut is a low-profile hex nut, typically from the Thin Series (DIN 439), that is used to lock a standard nut in place. By tightening a standard nut against a jam nut, you create internal tension between the threads of both nuts and the bolt. This “jams” the assembly together, providing a mechanical lock that prevents loosening caused by vibration or rotation.

Can a Thin Series nut handle the same torque as a Regular nut?

No. Because the Thin Series has fewer threads in contact with the bolt, it has a lower proof load. For M18 fasteners used in structural or high-stress environments, using a thin nut as the primary fastener could result in thread stripping or joint failure. Always use a standard height nut for primary load-bearing tasks.

Where are M18 nuts most commonly used?

M18 nuts are a “heavy-load” size often found in automotive truck suspensions, large agricultural equipment, and specialized construction machinery where M16 is insufficient but M20 exceeds the required space constraints.