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Westfield Fasteners Product Specification:

DIN 7982 - Pozi Countersunk Self Tapping Screws Type C

This product guide contains the specification for pozi countersunk self tapping screws, standard parts available from Westfield Fasteners. The basis of this specification is the DIN standard DIN 7982.

Product Description

Self tapping screws are normally used with sheet metal and plastics. This variant has a countersunk head with a pozi cross recess drive. The countersunk head is typically used in conjunction with a countersunk hole providing a flush, snag free fit. As the name suggests, this type of screw forms its own mating thread as it is installed into a pre-drilled hole.

There are many different types of screw that could be defined as 'self tapping', including several more modern designs. The self tapping screws defined here are the long established type adhering to DIN 7981. The same thread forms with differing head types are defined in other standards. These self tapping screws are manufactured in gauge sizes, from number 2 up to number 14, but these sizes are usually stated alongside the millimetre equivalent.

Scope of the DIN standard.

DIN 7982 specifies the tolerances and the variation in form of pozi countersunk self tapping screws, for sizes from No.2 (2.2 mm) up to and including No.14 (6.3 mm). Figure 1 and table 1 below define the overall dimensions and tolerances of this screw type. Table 2 defines the tolerance on the shank length. Although the DIN 7982 standard has now been superceded by ISO 7050, off the shelf parts are generally still manufactured to the older specification. The differences between the two standards include minor changes to the head heights and diameters to some sizes.

Self tapping screw thread forms have historically been classified in a number of different ways, and can cause some confusion. The DIN 7981 standard defines the thread form featuring spaced threads and a cone or pointed tip that we are concerned with here as a 'Type C'. This thread form is also known as 'Type AB' elsewhere. These type definitions help to differentiate these cone pointed tapping screws from the square ended or dog point 'Type F' (also known as 'Type B' or 'Type BZ', depending on who you ask).

In addition to the thread type codes outlined above, the drive is also given its own type: pozidrive is defined as 'type Z', whilst phillips is known as 'type H'.