Screw: It is the term used for a threaded fastener, with or without a head (headless – as in set screw) so designed as to permit it to be properly assembled in a pre formed internal threaded hole or capable of forming it’s own thread and secured by means of tightening the head.
Bolts: It is the term used for threaded fastener, with head, designed to be used in conjunction with a properly assembled by means of tightening a nut. Thus, the difference between a screw and a bolt is based on the ‘’DESIGN’’ capability of the threaded fastener, and not on actual service application.
A Standard Fastener: is one wich can be referenced from nationally recognized standards documents:
EXAMPLE 1 : hex bolt M10 x 1.50 x 50, class 8.8, zinc plated
EXAMPLE 2 ; hex cap screw ½-13 UNC x 4 2A SAE Grade 5, zinc plated