Generally fingertips head, coarse teeth, hard wood screws, but also for aluminum, plastic. For metal threaded hole open a special self-tapping screws are called wire-tapping.
Since 1914, self-tapping screws begin commercialization of the first, followed by the design ─ ─ primarily from wood screw tail cone system in the case of type A carburizing steel thread forming screws. Was the main purposes is used in the air conditioning system of the metal conduit engagement, so-called metal screws. After 80 years of development, a total can be divided into four periods ─ thread forming, thread cutting, thread rolling and self-drilling.

Thread forming self-tapping screws (Thread Forming Tapping Screws) ─ metal stainless steel screws directly by the Department of evolved, non-standard thread forming self-tapping screws used to be pre-drilled, and then screw into the hole, strong extrusion with female thread , while the original position in the female to the male of the materials will be squeezed between the threads, the thread forming what we called non-standard self-tapping screws. applied only to the thin and malleable material, so they developed; thread cutting tapping screw (Thread Cutting Tapping Screws) ─ the end of the thread cutting out one or more Road cutting mouth so screwed into pre-drilled holes in, the use of screw tail and dental unit in a similar way to the cutting of stainless steel screw tap out with overcast thread which can be used in thick, relatively hard or brittle materials such difficult shape of.


Self-tapping screws of non-standard dimensions, mechanical, functional performance of the following criteria:
ANSI / ASME B18.6.4 ─ Thread Forming And Thread Cutting Tapping Screws And Metallic Drive Screws (Inch Series)
SAE J933 ─ Mechanical and Quality Requirements For Tapping Screws
SAE J81 ─ Thread Rolling Screws
SAE J1237 ─ Metric Thread Rolling Screws
SAE J78 ─ Steel Self-Drilling Tapping Screws
FIP 1000 ─ Tapping Screws Performance Specifications
DIN 7500 ─ Thread Rolling Screws For ISO Metric Screws Thread
DIN 7504 ─ Self-Drilling Tapping Screws Dimensions, Requirements And Testing
ISO 2702 ─ Heat-Treated Steel Tapping Mechanical Properties
JIS B1055 ─ Mechanical Properties For Heat-Treated Steel and Stainless Tapping Screws


Here are the common types of teeth from the (metric) teeth (Inch)
A metric Tapping:
Specifications: ST 1.5, S T1.9, S T2.2, S T2.6, S T2.9, S T3.3, S T3.5, S T3.9, S T4.2, S T4.8, S T5.5, S T6.3, S T8.0, S T9.5
Pitch: 0.5,0.6,0.8,0.9,1.1,1.3,1.3,1.3,1.4,1.6,1.8, 1.8,2.1,2.1
2 Inch Tapping:
Specifications: 4 #, 5 #, 6 #, 7 #, 8 #, 10 #, 12 #, 14 #
Number of teeth: AB teeth 24,20,20,19,18,16,14,14
A teeth 24,20, 18, 16,15,12,11,10