M3 Nut Dimensions: Hex & Thin Series

Q: What size wrench or spanner do I need for an M3 nut?

An M3 hex nut requires a 5.5 mm wrench or socket. The standard width across flats (s) for an M3 nut is 5.50 mm. This is a very common tool size found in electronics toolkits and hobbyist driver sets.

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. If subjected to the high torque levels intended for a standard bolt, the threads within a thin nut are more likely to strip. Always use a standard height nut for structural or high-tension applications.

Q: Why is M3 the most popular “small” metric nut?

M3 is considered the industry standard for small-scale consumer goods. It offers a perfect balance between strength and size, making it the go-to fastener for mounting cooling fans, securing internal electronics, and as the primary fastener in DIY desktop 3D printers.

M3 nut dimensions or sizes are critical for 3D printer assembly, computer chassis components, and robotics modules. This size is specifically engineered to mate with fasteners having a 3.00 mm nominal diameter and is available in M3 x 0.5 for the coarse series and M3 x 0.35 for the fine series, where 0.5 and 0.35 represent the thread pitch in millimeters.

This chart 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 standard 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

M3 x 0.5 Hex Nut – DIN 13-1/ISO 68-1
Dimension	Size (mm)
Dimension	Min	Max
Major Diameter	3	3.172
Pitch Diameter	2.675	2.775
Minor Diameter	2.459	2.599
Thread Pitch	0.5

M3 x 0.35 Hex Nut – DIN 13-21/ISO 68-1
Dimension	Size (mm)
Dimension	Min	Max
Major Diameter	3	3.141
Pitch Diameter	2.773	2.863
Minor Diameter	2.621	2.721
Thread Pitch	0.35

M3 Hex Nut – DIN 934/ISO 4032 & ISO 8673
Diameter	3	3.45
Width Across Flats	5.32	5.5
Width Across Corners	6.01	Not specified
Height / Thickness	2.15	2.4

M3 Thin / Half Nut – DIN 439/ISO 4035 & ISO 8675
Diameter	3	3.45
Width Across Flats	5.32	5.5
Width Across Corners	6.01	Not specified
Height / Thickness	1.55	1.8

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Frequently Asked Questions

What size wrench or spanner do I need for an M3 nut?

An M3 hex nut requires a 5.5 mm wrench or socket. The standard width across flats (s) for an M3 nut is 5.50 mm. This is a very common tool size found in electronics toolkits and hobbyist driver sets.

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. If subjected to the high torque levels intended for a standard bolt, the threads within a thin nut are more likely to strip. Always use a standard height nut for structural or high-tension applications.

Why is M3 the most popular “small” metric nut?

M3 is considered the industry standard for small-scale consumer goods. It offers a perfect balance between strength and size, making it the go-to fastener for mounting cooling fans, securing internal electronics, and as the primary fastener in DIY desktop 3D printers.