All the fasteners listed on our website are listed in the following format:
Diameter of shank/threads (plus thread pitch if applicable) x length followed by the drive type and usage/type.
For example: 1/4"-20 x 2" Square Head Machine Bolt
This describes a 1/4 inch diameter shank with 20 threads per inch (aka coarse thread) having a square head drive that accepts a nut and is 2" long from the underneath of the head to the end of the shank.
Some fasteners such as wood screws will be measured by their "gauge size." Please refer to this chart to determine the diameters that correspond to their gauge size: Screw Dimensions
We sell a simple gauge that can measure the diameter and length of screws under 1/2" in diameter and under 3" in length: