Screw designation and thread determination

The designation of standardized screws follows a rule: first the DIN is mentioned, followed by the diameter and screw length in millimeters. The DIN or additional text information defines the drive of the screw, which can be used to determine the appropriate screwdriver or bit.

Tip: The screw length is measured up to below the screw head, because the head usually protrudes after assembly, but countersunk screws are an exception: here the screw length is measured INCLUDING THE HEAD, because the screw sinks into the component.

To complete the screw connection, you need not only the right tools but also the right accessories such as washers and nuts. While the inside diameter of the washers reflects the outside diameter of the screws, it is important to pay attention to which thread you find with the nuts. If it is metric, you need the appropriate counterpart in M ​​(followed by the diameter). If it is a sheet metal thread, you can only use nuts with a sheet metal thread. For inch screws, you need nuts with the appropriate inch thread. Example: For an inch screw with diameter No. 4 you can never use a nut with the metric dimension M4!

 We refer here to our table “Drives and head shapes”.

The designation of American inch screws, on the other hand, is made up of the respective standard, which determines the head shape, followed by the type of thread (coarse thread / fine thread), the diameter, the number of thread turns per 1 inch and the length.

Example:

UNC 1/4"-20x1" refers to a coarse thread with a diameter of ¼" inch, 20 threads per 1 inch and a length of 1", which would also include the head height of a countersunk screw.