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Self Tapping Screws

These screws are different as compared to the conventional type. The difference between them is that the design of the self-tapping type taps their threads when screwed into a material such as plastic, brick, wood, or metal. This type of fasteners is commonly used during the attachment of two pieces of components together, especially if the user has access to only one side of the material. These fasteners prove to be useful when the product has to be either disassemble or reassemble products. For example, in the reassembly of furniture, a stainless steel threaded fastener of this variety, will be able to relocate themselves into the same threads from where their extraction point. It is a pre-requisite to choose the correct sized ones, to prevent thread stripping while ensuring a secure fastening to the material. Making an ideal choice for the appropriate size of the fastener entails taking into account the length of the fasten tip, according to the thickness of its material. The presence of adequate space is required for the tip of the drilled fastener to enter the component before the threading begins.

These threaded fasteners are categories into two variants based on the construction of their tips that is thread forming and thread tapping.

Thread-forming type:- Before using these fasteners, a pilot hole is required to be drilled since the said screw itself does not contain a pointed tip. Thread-forming variety is typically associated with joining plastic materials together. Due to their design, these fasteners have a much tighter grip on the component. There is a risk of over-tightening them, which is why the worker using them must handle them with care. Over tightening these fasteners can result in the breaking of joined materials from the pressure.

Thread-Tapping type:- Although this kind of threaded fastener does not require a pilot hole, drilling one makes its fastening easier. It is mandatory to drill a smaller pilot hole as compared to the diameter of a thread tapping type. The reason behind drilling a smaller pilot hole is because thread-tapping variety of fastening tends to eliminate material while creating a path for it. One drawback to using the thread tapping type is their removal often leads to the resultant material having stripped threads.

These threaded fasteners could also be segregated based on the construction of their heads. Two of the most commonly used types include countersunk and Allen or socket head kind. Apart from these heads, the other forms of screws include the following Bugle head, Flange head, Button head, Wafer head, Hex head, dome head, Truss head & Squarehead. Although the construction of the head varies, their tip could be either the thread forming or the tapping variety.

Production includes different materials like carbon steel, alloy steel, Hastelloy, Monel, nickel, Inconel as well as duplex steels. However, the most commonly preferred material are the various grades of Stainless Steel. Based on their utility, they could be surface treated with zinc or anti-rust oil, black paint, etc.
Head Style
Self Tapping Screws Head Style
DIN 7982 Screws Dimensions & Sizes
DIN 7982 Self Tapping Screw Sizes
    (S) No. Size
    (L) Thread diameter often 5%  smaller
    (in mm)
     Approx. Head Diameter
    (in mm)
    No 2 2.2 2.9
    No 4 2.9 5.3
    No 6 3.5 6.6
    No 8 4.2 7.3
    No 10 4.8 9.3
    No 12 5.5 10.5
    No 14 6.3 12.2
Standard Specification
Material A2 / A4 Stainless Steel, Carbon steel, Copper, Brass
  • Thread-Cutting Screws (TCS)
  • Thread Rolling Screws (TRS)
Head Type Any head style
Point Type Any point style
Standard No. DIN7981 FZ
ISO Standard ISO 7049
Head Pan
Diameter ST2.2, ST2.9, ST3.5, ST3.9, ST4.8, ST4.2, ST5.5, ST6.3, ST8, ST9.5
Length 4.5, 6.5, 9.5, 13, 16, 19, 25, 30, 32, 38, 50
DIN 7981 C - TYPE AB DIN 7981 C, UNI 6954, ISO 7049, CSN 21235
Material Forming Cutting Self Drilling
Sheet Metal 0.015" to 0.050" Thick (Steel, Aluminium, Brass etc.) TYPE A TYPE B HEX HEAD TYPE B SWAGE FORM   TYPE 21   TAPITS
Stainless Steel 0.015" to 0.050" Thick (A2/ A4) TYPE A TYPE B HEX HEAD TYPE B SWAGE FORM   TYPE 21 TYPE F  
0.015" to 0.200" Thick (Steel, Aluminium, Brass etc.)   TYPE B HEX HEAD TYPE B SWAGE FORM TYPE U TYPE 21 TYPE F  
Structural Steel 0.200" to 1/2" Thick     HEX HEAD TYPE B SWAGE FORM TYPE U   TYPE F  
Thread Rolling Self Tapping Screw Dimensions
Screw Length C D G
Screw Dimensions Point
Circumscribing Circle Dia. Measurement Acrose Center Circumscribing Circle Dia.
Maximum Minimum Maximum Minimum Maximum
4-40 0.1105 0.1095 0.1055 0.090
6-32 0.1410 0.1350 0.1350 0.1290 0.111
8-32 0.1670 0.1610 0.1610 0.1550 0.137
10-24 0.1940 0.1880 0.1860 0.1800 0.153
10-32 0.1930 0.1870 0.1870 0.1810 0.163
1/4-20 0.2550 0.2490 0.2450 0.2390 0.206
5/16-18 0.3180 0.3120 0.307 0.301 0.264
3/8-16 0.3810 0.3750 0.3685 0.3625 0.320
Nominal Length of Screw
Length Tolerance Screw Nominal Size To 1/2 - 1" Inclusive Over 1/2 - 1" Inclusive Over 1 - 2" Inclusive Over 2"
#4 - #10 +0. - .030 +0. - .030 +0. - .060 +0. - .090
1/4" - 3/8" +0. - .030 +0. - .030 +0. - .060 +0. - .090