Bolts come in standardised sizes that are measured based on the physical dimensions of the bolt. These sizes are based on the style and size of the bolt. Bolt measurements also include the number of threads that the bolt has compared to its length.
The length of a bolt is measured according to the bolt's usable length. Parts of the bolt that stick out from a surface it is sunk into are not counted in this measurement. For standard bolts, length is given in inches.
Bolt diameter is measured based on one of three dimensions. Thread diameter measures the bolt's width based on the diameter of the threaded part of the bolt. Shank diameter measures the non-threaded shank of the bolt below the head. Root diameter is equal to the width of the shank without its threads. The type of measurement used depends on the type of bolt.
Thread count is measured in the number of threads per inch along the threaded part of the bolt;s shaft. Bolts with a large number of threads per inch are considered fine threaded bolts. Bolts with relatively few threads per inch are coarse threaded.
Metric bolts use the term thread pitch to denote the frequency of threads on a bolt. Metric bolts measure the distance between threads. Metric bolts with threads spaced closely are called fine pitch. Bolts with threads far apart are coarse pitch.