Screw threads

A helical groove cut into outside surface of cylindrical rod (studding) on he shank of a fastener such as a bolt or screw with a head slotted, hexagonal or other designs to allow tightening using a tool or the inside of a cylinder or cone. Before 1841 screw threads were not standardised but manufactured by hand or machined to individual design. In 1841 Sir Joseph Whitworth devised the Whitworth thread series this standardised the diameter of the thread, its pitch, axis and number of threads per inch. Single the development of the notion of standardisation a number of thread systems have been developed and these are:

BSW British Standard Whitworth
BA British Association 0 15BA
BSF British Standard Fine
BSWS British Standard Whitworth Small
BSP British Standard Pipe
BSC British Standard Cycle
UNC
CSS Sellers or American Standard
SI Systeme Internationale (metric thread)
M Metric Thread
Edison-type threads
Work threads
ACME Standard Screw thread

Threads can easily be cut by hand using a tap or die or machined using a lathe, milling, grinding or rolling.