Self-tapping screw is one of the threaded fasteners pre-drilled strike out in metal or nonmetal material. It has high tensile, single and unilateral combination characteristic. Self-tapping screw materials can be divided into carbon steel and stainless steel two kinds. Usually, it is made by 1022 medium carbon steel.

Classification:

1. According to different heads, it can be divided into: round head, flat head (that is, countersunk head), shore head, dome wide edge head, great circle head (that is, large flat head), hex socket head, hex socket hole washer head, hexagon head.
2. According to the troughs, there are word slotted head type (also called slot), phillips head type, 11 words compound type and M words type.
3. According to standard, it can be divided into: GB, German standard (DIN), American standard (ANSI), British standard (BS).

Philips countersunk head tapping screw specification

Standard: Cross slot GB845-85 GB846-85 GB847-85 JIS1122
Materials: Carburizing steel stainless steel
Surface: Galvanized

GB846-85 Philips countersunk head tapping screw
Carburizing steel stainless steel L<=50mm L>50mm Thread length according to the agreement
Thread Specification		ST2.2	ST2.9	ST3.5	ST4.2	ST4.8	ST5.5	ST6.3
dk max		3.8	5.5	7.3	8.4	9.3	10.3	11.3
K  max		1.1	1.7	2.35	2.6	2.8	3	3.15
m	H	1.9	3.2	4.4	4.6	5.2	6.6	6.8
	Z	2	3.2	4.3	4.6	5.1	6.5	6.8
Slot number		0	1	2	2	2	3	3
L		4.5-1.6	6.5-19	9.5-32	13-38	16-45	19-50	22-75