This is a machine screw with a length of 3/4 inches. We generally use this to secure roller chain, but can be used for many applications, such as mounting electronics. This mates with our #4-40 nut
The 40 in the 4-40 is the number of threads per inch. This is UNC (Unified National Coarse) thread pitch. The pitch is .025 inches from crown to crown. The major diameter is .1075. The length of the screw of 3/4 inches does not include the pan head portion of the screw. Including the pan head portion, the screw length is 0.81 inches.