What do the letters and numbers on the screw head mean?

Letters and numbers on the screw head indicate thread parameters, as shown below:

First, the letter said:

Answer: Mechanical screws: Mechanical screws.

B: self-tapping screws:? Self-tapping screws (for metals and plastics)

B- 1: metal plate tapping screw. (Iron plate tapping screw)

B-2: plastic self-tapping screws. Self-tapping screws for plastics

C: wood screws: woodworking screws

D: drywall screws: cement wall screws.

E: Self-drilling screws? Drill tail screws (stainless steel drill tail screws, composite drill tail screws)

Second, the digital representation:

1: stainless steel plate, metal steel plate, galvanized steel plate, engineering installation.

2. Indoor and outdoor installation, such as metal curtain wall and light metal compartment.

3: General angle steel, channel steel and iron plate are installed in combination with other metal materials.

4. Assembly engineering of automobile trunk, container, shipbuilding and refrigeration equipment.

Note: In the standard thread marking method stipulated by national standards, the first letter represents the thread code, such as m for common thread, g for pipe thread without thread seal, r for pipe thread with thread seal, and Tr for trapezoidal thread. The second number represents the nominal diameter of the thread, which is the main diameter of the thread. It represents the maximum diameter of the thread in millimeters.

Extended data:

Main geometric thread parameters of screws:

1, outer diameter (large diameter), the diameter of an imaginary cylinder coincident with the top of external thread or the bottom of internal thread. The nominal diameter of the thread is the large diameter.

2. Inner diameter (small diameter), the imaginary cylinder diameter that coincides with the bottom of external thread or the top of internal thread.

3, middle diameter, the bus bar passes through the imaginary cylinder diameter with the same width as the convex and groove on the tooth profile.

4. Pitch, the axial distance between two points corresponding to adjacent teeth on the pitch line.

5. Lead, that is, the axial distance between two points corresponding to adjacent teeth on the same helix on the pitch diameter line.

6. Tooth profile angle, the included angle between two adjacent sides on the thread profile.

7, thread angle, the angle between the tangent of the helix on the medium diameter cylinder and the plane perpendicular to the thread axis.

8. Working height, the distance between overlapping parts on the matching thread profile in the direction perpendicular to the thread axis, etc. The nominal diameter of the thread is the nominal diameter except the internal diameter of the pipe thread, and the external diameter is the nominal diameter. Threads have been standardized, including metric and English. The international standard adopts the metric system, and China also adopts the metric system.

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