What is the difference with ordinary screws

Update:29 Jan 2019
Summary:

Self-tapping screws are threaded fasteners that are sel […]

Self-tapping screws are threaded fasteners that are self-tapping in the pre-drilled holes of metal or non-metallic materials. Self-tapping screws feature high tensile, single-piece, single-sided combinations. Self-tapping screws are often used for connections between thin metal sheets (steel plates, sawing boards, etc.). When connecting, first make a threaded bottom hole for the connected piece, and then screw the self-tapping screw into the threaded bottom hole of the connected piece. Since the threaded surface of the tapping screw has a high hardness (≥45HRC), the internal thread can be tapped in the threaded bottom hole of the connected member to form a joint.

The shape of the self-tapping screw head has a round head, a flat head, a semi-recessed head and a countersunk head. The material is generally carburized steel, and the surface hardness of the material after heat treatment is not less than 45HRC.

Compared with the threads of ordinary screws, the pitch is large and the small diameter is slightly smaller at the same large diameter, which has been standardized. Self-tapping screws can be divided into carbon steel and stainless steel. Carbon steel materials are usually made of 1022 medium carbon steel. Usually used on doors and windows, iron sheets. The head is a bearing surface formed by one end of the enlarged shape. For the thread forming and thread cutting self-tapping screws (self-tapping screws), the flat top countersunk, the flat head, the pan head, the hexagonal and the hexagonal wire The most important of the heads, these five head types account for almost 90% of all self-tapping screws, the use of self-tapping screws (self-tapping screws) should be considered first.

The other five other types are flat top concave bearing surface, flat top full edge, oblate concave bearing surface, oblate round edge and cylindrical head for relatively minor head shape, and incense top countersunk. Thread rolling into self-tapping screws (since The choice of the head type is the same as the above. The main consideration is that the mushroom head, the round head and the 100-degree flat top are not taken for the new design. The function of the head can be replaced by other head types. The pan head can replace the mushroom head and Round head, 82 degree flat top counters can replace 100 degrees flat flat top, flat dome, pan head, hexagon head and hexagonal head.

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