M20 Nut Dimensions: Hex & Thin Series

Q: What size wrench or spanner do I need for an M20 nut?

An M20 hex nut typically requires a 30 mm wrench or socket. The standard width across flats (s) for an M20 nut is 30.00 mm. Due to the high torque requirements of M20 fasteners, heavy-duty impact sockets or long-handled spanners are generally required for proper tensioning.

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 M20 applications, which often involve critical structural loads, using a thin nut as the primary fastener is unsafe as the threads are likely to strip or fail under high tension. Always use a Regular Series nut for primary load-bearing joints.

M20 nut dimensions or sizes are critical for bridge construction, heavy-duty industrial framing, and large engine mounting. This size is specifically engineered to mate with fasteners having a 20.00 mm nominal diameter and is available in M20 x 2.5 for the coarse series and M20 x 1.5 for the fine series.

This charts is based on 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 high-capacity 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

M20 x 2.5 Hex Nut – DIN 13-1/ISO 68-1
Dimension	Size (mm)
Dimension	Min	Max
Major Diameter	20	20.585
Pitch Diameter	18.376	18.6
Minor Diameter	17.294	17.744
Thread Pitch	2.5

M20 x 2.0 Hex Nut – DIN 13-21/ISO 68-1
Dimension	Size (mm)
Dimension	Min	Max
Major Diameter	20	20.501
Pitch Diameter	18.701	18.913
Minor Diameter	17.835	18.21
Thread Pitch	2.0

M20 x 1.5 Hex Nut – DIN 13-21/ISO 68-1
Dimension	Size (mm)
Dimension	Min	Max
Major Diameter	20	20.406
Pitch Diameter	19.026	19.216
Minor Diameter	18.376	18.676
Thread Pitch	1.5

M20 x 1.0 Hex Nut – DIN 13-21/ISO 68-1
Dimension	Size (mm)
Dimension	Min	Max
Major Diameter	20	20.304
Pitch Diameter	19.35	19.51
Minor Diameter	18.917	19.153
Thread Pitch	1.0

M20 Hex Nut – DIN 934/ISO 4032 & ISO 8673
Diameter	20	21.6
Width Across Flats	29.16	30
Width Across Corners	32.95	Not specified
Height / Thickness	16.9	18

M20 Thin / Half Nut – DIN 439/ISO 4035 & ISO 8675
Diameter	20	21.6
Width Across Flats	29.16	30
Width Across Corners	32.95	Not specified
Height / Thickness	9.1	10

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Frequently Asked Questions

What size wrench or spanner do I need for an M20 nut?

An M20 hex nut typically requires a 30 mm wrench or socket. The standard width across flats (s) for an M20 nut is 30.00 mm. Due to the high torque requirements of M20 fasteners, heavy-duty impact sockets or long-handled spanners are generally required for proper tensioning.

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 M20 applications, which often involve critical structural loads, using a thin nut as the primary fastener is unsafe as the threads are likely to strip or fail under high tension. Always use a Regular Series nut for primary load-bearing joints.