Necessary Knowledge Of Fasteners - Nuts

01. Imperial nut

According to ANSI/ASME B18.2.2, ANSI/ASME B18.6.3. (machine nut), BSW916, JIS B 1181.

According to its characteristics, it can be divided into: ordinary nuts (FINISHED HEX NUTS) (1/4 or more including 1/4 specifications)––FIN;

Thin nuts (FINSHED HEX JAM NUTS) ((1/4 above including 1/4 specifications)––JAM;

Heavy-duty nuts (HEAVY HEX NUTS) (above 1/4 including 1/4 specifications)––HVY;

Machine nut (MACHINE SCREW NUTS) (#4-40-3/8 specification)–– M/S;

The difference between American-made nuts: ordinary, heavy, and thin nuts can be manufactured in specifications of 1/4-1 1/2, and mechanical nuts can be manufactured in specifications of 3/8 or less. The difference between imperial nuts is mainly in thickness, and the opposite sides are also slightly different.

① Thin nuts are the same as ordinary nuts, but the thickness of thin nuts is smaller than that of ordinary nuts.

②Mechanical nuts have larger opposite sides than ordinary nuts, larger thickness than thin nuts, and smaller than ordinary nuts.

③The opposite side of the heavy-duty nut is larger than that of the mechanical nut, and the thickness is thicker, and its thickness is slightly smaller than the nominal diameter.

Now take the 3/8 nut as an example:

The difference between British Webster nuts (BSW916 and JIS B 1181):

02. Metric nuts

Differences in standards: old national standard, new national standard, international standard, German standard, Italian standard

Note: The dimensions in the table are the upper limit of the specification

The reference standards are as follows:

product identification

01. Diagram of each part of the nut:

02. Nut identification

performance level

Nuts with performance grades ≥ 8 and 05 must be marked with concave characters on their supporting surfaces or sides, or marked with raised characters on the chamfered surface, and only hexagonal nuts with a thread diameter ≥ 5mm need to be marked

Types of Nut Threads

01. Thread type

There are many types of threads formulated for various countries, such as:

M - metric coarse teeth, fine teeth, very fine teeth

UNC - United Coarse (Imperial)

UNF - United fine tooth (imperial system)

W——Wechsler's coarse teeth, fine teeth (JIS)

In addition, there are 8 thread series (8-UN) and 12 thread series (12-UN) in the imperial system.

02. Thread accuracy grade

① Metric system (DIN, ISO, GB) is divided into 6H, 6G grades. Usually it is 6H level. The Japanese Metric Standard (JIS) is divided into three types: Class I, Class II, and Class III. The usual condition is grade II.

②The British system is 1B, 2B, and 3B. Generally, it is 2B grade.

③At present, there are two kinds of tooth angles used for tapping: 600 and 550, 600 has metric teeth, British UNC UNF, etc., 550 has Webster teeth and BSW, BSF, etc.

④ The main geometric parameters of the thread are: thread major diameter, pitch, thread pitch diameter, and thread ascending angle. The above points all affect the thread accuracy.

Relevant requirements for hot-dip galvanized nuts

Due to the thicker hot-dip galvanized coating (generally above 40um), considering its influence on thread accuracy, the hole diameter of hot-dip galvanized nuts must be slightly enlarged than ordinary nuts when forming: