SCREWS

Countersunk screws are also called Flat head or CSK screws. These screws have a flat head which tapers along the shaft.

Flat head screws are used for flush mounting of sections, usually where one part slides over another or one part is mounted on another. They are used with a countersunk hole to provide a flush, snag free fit.

Countersunk head screws, like button heads and low heads, are limited by configuration in their tensile strength capability. Because of this, they should not be used in applications requiring full strength, where Socket Head Cap Screws should be used.

Flat head screws require a matching counter in the workpiece.

The Countersunk head is preferred to obtain a flush and level finish without any projection in metal or plastic. They sink into the surface to give a smooth exterior finish.

The head angle for metric countersunk socket screws is 90 degrees up to & including M20 and 60 degrees over M20.

The head angle for Imperial is different – Unified is 82 degrees and British thread forms are 90 degrees.