Understanding screw size is crucial to choosing the right screws for your project. By considering key metrics like length, diameter and pitch, you can ensure that the screw will fit its intended application.

Screw size is commonly described by three figures – the gauge, threads per inch (TPI) and length in inches or millimeters. This system is widely used in the United States and most other countries that utilize imperial units. However, metric systems are also becoming more prevalent and these screws will be marked with an M prefix.

The first number, called the gauge, refers to the screw’s basic diameter. This is determined by measuring the distance from the crest of one thread to the trough of the next on one side of the screw, and then comparing this measurement with a screw gauge chart. Screws with oval heads are an exception, and their diameter is measured from the widest point of the head.

The second number is the screw’s thread pitch, which is measured by counting the number of threads in an inch of length. This is important because threads with different pitches create different levels of grip, which can impact the strength and ease with which a screw is installed. Screws with a lower pitch have coarser threads, while those with a higher pitch have finer ones. #6 screw size