The letters and numbers on the screw head indicate the thread parameters as follows:

1. Letters indicate:

A: Machine Screw: machine screw

B: Tapping Screw:? Self-tapping screw (used in metal and plastic respectively)

B-1: Sheet Metal Tapping Screw. (iron tapping screw)

B-2: Plastic Tapping Screw. (tapping screw for plastic)

C: Wooden Screw: woodworking screw

D: Drywall Screw: cement wall screw. Drill tail screw (stainless steel drill tail screw, composite drill tail screw)

2. 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 works of automobile trunk, container, shipbuilding industry, refrigeration equipment, etc.

note: in the standard thread marking method stipulated by national standards, the first letter represents the thread code, for example, m represents common thread, g represents pipe thread sealed by non-thread, r represents pipe thread sealed by thread, and Tr represents trapezoidal thread. The second number indicates the nominal diameter of the thread, which is the major diameter of the thread. It represents the maximum diameter of the thread in millimeters.

Extended information:

Main geometric thread parameters of the screw:

1. Outer diameter (large diameter), the diameter of an imaginary cylinder which coincides with the top of the external thread or the bottom of the internal thread. The nominal diameter of the thread is the major diameter.

2. Inner diameter (small diameter), which is the diameter of an imaginary cylinder coincident with the bottom of external thread or the top of internal thread.

3. Middle diameter: the diameter of an imaginary cylinder with the same width of the convex and groove on the tooth profile.

4. Pitch, that is, the axial distance between two points corresponding to the middle diameter line of adjacent teeth.

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

6. Tooth profile angle, which is the included angle between two adjacent flanks on the thread profile.

7. Thread elevation angle, which is the included 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 the overlapping parts of the two matched thread profiles 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 system and English system. The international standard adopts the metric system, and China also adopts the metric system.

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