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.
Generally used in electrical or radio work, these fasteners are slightly undercut under the head. That provides the ability to bind stranded wire tightly and prevent fraying. Common applications for slotted screws include woodworking, although the drive style is not designed to be used with power drivers.
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.