Hex Nuts - JIS-standardized hex nuts with selection information

Hex nuts (also known as hex nuts) are an essential fastener in the mechanical engineering industry. Thanks to their six wrench flats and standardized dimensions, they allow for secure and easy installation using appropriate tools such as open-end, ring, or socket wrenches. When used in conjunction with a matching threaded screw or bolt, they form a mechanically stable connection: the screw joint.

Many countries, including Japan, have standards governing the specifications of these nuts. This article will focus on the Japanese JIS standard and discuss what it entails for hex nuts.

What are hex nuts, and how are they used?

Hex nuts are among the most important fasteners in industry and trade. They are frequently used in combination with screws and washers to create a secure connection between two or more components.

The hexagonal shape offers the advantage of easy installation using a matching wrench or socket wrench. The six sides ensure a secure grip, as the tool cannot slip as easily as with other nut shapes.

To increase the load-bearing capacity of the connection, it is advisable to use a suitable washer. This distributes the forces evenly over a larger area, thereby protecting the components from damage and preventing loosening due to vibrations.

What is the JIS standard for hex nuts?

The Japanese Industrial Standard (JIS) is a set of standards developed by the Japanese government to ensure that products manufactured in Japan meet a consistent level of quality. The JIS specifies technical requirements for many different types of products, including hex nuts.

The JIS standard for hex nuts states that they must be manufactured in sizes ranging from M3 to M52. They must have specific standard dimensions relating to height, head diameter, outer edge dimensions, and thread pitch. The standard also defines the materials that may be used for the manufacture of hex nuts, such as steel, brass, and stainless steel.

Why is compliance with the JIS standard important?

Compliance with the JIS standard is important because it helps ensure that hex nuts are safe and reliable. Since the nuts have specific standard dimensions, they are easy to integrate into various machine parts. This enables proper assembly and ensures that the machine parts function correctly. The guidelines for permissible materials also ensure that the hex nuts are robust and durable.

When selecting hex nuts, it is important to consider the specifications of the components and materials.

The DIN specifications commonly used in Europe or the JIS specifications originating from Japan can serve as a basis for this. However, it is important to note that not all components and materials are compatible between JIS and DIN.

It is therefore recommended to adhere to the specifications of a single region when selecting precision components to be combined with one another.

Hex nut, Type 1 – Standard thread (first choice) Shape and dimensions

1 - Chamfer on both sides / 2 - With flat surface

* - Reference

Source: JIS B 1181(2014)

Shapes and dimensions of hexagon nuts type Ⅰ (product class A) - extract from JIS B 1181(1995) - unit: mm
Thread Nominal Ø
Ø (d)		 M 2 M 3 M 4 M 5 M 6 M 8 M 10 M 12 (M 14) M 16
Slope P 0.4 0.5 0.7 0.8 1 1.25 1.5 1.75 2 2
c Max. 0.2 0.4 0.4 0.5 0.5 0.6 0.6 0.6 0.6 0.8
Min. 0.1 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.2
a Min. (Reference dimension) 2 3 4 5 6 8 10 12 14 16
Max. 2.3 3.45 4.6 5.75 6.75 8.75 10.8 13 15.1 17.3
w Min. 3.07 4.6 5.9 6.9 8.9 11.6 14.6 16.6 19.6 22.5
e Min. 4.32 6.01 7.66 8.79 11.05 14.38 17.77 20.03 23.35 26.75
m Max. (Reference dimension) 1.6 2.4 3.2 4.7 5.2 6.8 8.4 10.8 12.8 14.8
Min. 1.35 2.15 2.9 4.4 4.9 6.44 8.04 10.37 12.1 14.1
mI Min. 1.08 1.72 2.32 3.52 3.92 5.15 6.43 8.3 9.68 11.28
s Max. (Reference dimension) 4 5.5 7 8 10 13 16 18 21 24
Min. 3.82 5.32 6.78 7.78 9.78 12.73 15.73 17.73 20.67 23.67
Notes: 1. The nominal thread diameter stated in parentheses should only be used if absolutely necessary.
2. Unless otherwise specified, the shape of the nuts is "bevel on both sides"/"bevel on one side" and must be specified by the buyer.
The bevel dimensions of the upper side of the thread area with "bevel on one side" must have the same dimensions as for "bevel on both sides".
* On some of the currently supplied M10 and M12 hexagon bolts and nuts, the opposite side S is based on an earlier version of the JIS standard.

Note

  • M1.6 and M2.5 have been added compared to the previous standard JIS B 1181 (1993).
  • Some hex nuts, M10 and M12, currently in circulation have the opposite side s according to the old JIS.

Hex nut - Style 2 - Coarse thread Shape and dimensions

1 - Chamfer on both sides / 2 - With flat surface

* - Reference

Source: JIS B 1181(2014)

Shapes and dimensions of hexagon nuts type Ⅱ (product class A) - extract from JIS B 1181(1995) - unit: mm
Thread Nominal Ø
Ø (d)		 M 5 M 6 M 8 M 10 M 12 (M 14) M 16
Slope P 0.8 1 1.25 1.5 1.75 2 2
c max. 0.5 0.5 0.6 0.6 0.6 0.6 0.8
Min. 0.15 0.15 0.15 0.15 0.15 0.15 0.2
a Min. (Reference dimension) 5 6 8 10 12 14 16
  Max. 5.75 6.75 8.75 10.8 13 15.1 17.3
w Min. 6.9 8.9 11.6 14.6 16.6 19.6 22.5
e Min. 8.79 11.05 14.38 17.77 20.03 23.35 26.75
m Max. (Reference dimension) 5.1 5.7 7.5 9.3 12 14.1 16.4
Min. 4.8 5.4 7.14 8.94 11.57 13.4 15.7
mI Min. 3.84 4.32 5.71 7.15 9.26 10.7 12.6
s Max. (Reference dimension) 8 10 13 16 18 21 24
  Min. 7.78 9.78 12.73 15.73 17.73 20.67 23.67
Notes: 1. The nominal thread diameter stated in parentheses should only be used if absolutely necessary.
2. Unless otherwise specified, the shape of the nuts is "bevel on both sides"/"bevel on one side" and must be specified by the buyer.
The bevel dimensions of the upper side of the thread area with "bevel on one side" must have the same dimensions as for "bevel on both sides".
* On some of the currently supplied M10 and M12 hexagon bolts and nuts, the opposite side S is based on an earlier version of the JIS standard.

Note

  • Some hex nuts, M10 and M12, currently in circulation have the reverse side (s) according to the old JIS standard.