Zinc Plated Steel Machine Screw, Pan Head, Phillips Drive, #4-40, 3/8" Length (Pack of 100)

Machine Screws, also referred to as Machine Bolts, are often used with nuts or driven into tapped holes. They come in a variety of head types and drive styles, but are generally available in smaller sizes.

Steels are designated by a 4 number SAE Steel grade.  The first two digits indicate the primary materials used to form the steel.  The last 2 digits identify the percentage of carbon for the alloy (in hundredths).  The steel used in these fasteners has a tensile strength ranging from 100,000 to 150,000 psi (pounds per square inch).  Zinc Plating helps to prevent corrosion.

Pan head fasteners have a low, large cylindrical head with a high rounded top edge for higher tightening torques - these fasteners are often recommended to replace older head styles such as round, binding, or truss-head where possible. The Phillips drive style was originally designed so that the driver would slip out under extreme torque, preventing over-tightening and damage to the fastener or the material.

A threaded fastener's size name includes information about the major external diameter, followed by the threads per inch, which indicates if it is coarse or fine. Coarse threads are better when working with brittle materials; they are sturdier and are easier to thread and unthread compared to fine. Coarse threading also allows for thicker coatings and platings.