Marking on the head of the bolt is not a mandatory requirement. Because the mark on the head of the bolt is generally marked according to the manufacturer's own standards, the information indicated by these marks is not uniform.
There are generally the following possibilities:
Indicates the mechanical grade of the bolt, for example: 8.8, 10.8
Indicates thread specifications, for example: M42*2, G3/8
There is also the manufacturer’s code or manufacturer’s product model.
A——means: Machine Screw
B-means: Tapping Screw
B-1——means: Sheet Metal Tapping Screw
B-2——means: Plasic Tapping screw
C-means: Wooden Screw
D-means: Drywall Screw
E-means: Self Drlling Screws
1-means: stainless steel plate, metal steel plate, galvanized steel plate, engineering installation.
2-Means: indoor and outdoor installations such as metal curtain walls and metal light partitions.
3-Means: General angle steel, channel steel, iron plate and other metal materials are combined and installed.
4——Assembly engineering of representation, car trunk, container box, shipbuilding industry, refrigeration equipment, etc.
The outer diameter of the metric thread is in millimeters, such as 6, 8, 10, 12, 18, and 20 mm and the pitch is also in millimeters, such as 0.5, 0.75, 1, 1.5, 2, 3, etc.
The outer diameter of the inch thread is in inches, and each inch is equal to 25.4 mm, such as: 3/16, 5/8, 1/4, 1/2, etc., so the reading of the outer diameter with a metric ruler often contains irregular decimals.
The imperial pitch is expressed by the number of teeth per inch. Set the caliper at 25.4 mm, and align one ruler tip with the thread tip, and the other ruler tip will be inch thread if it is aligned with the thread tip. If the thread tip is not aligned, it should be a metric thread.
When measuring the thread pitch, it is best to print the tip of the thread on the white chalk. The mark on the chalk is clear and easy to measure. To measure the metric screw pitch, you should measure a length, such as 10, 15, 20 mm, etc., count how many teeth it contains, and calculate the pitch.
The thread specifications specified in inches are inch threads, such as G1". The thread specifications specified in millimeters are metric threads, such as M30.
The imperial system is determined by how many teeth there are in one inch (2.54 cm), generally 55 degrees, and the metric system is the pitch of the pitch determined by the distance between the two tooth tips, generally 60 degrees.