Owner's manual
3
1
.
Basic
i
n
th
r
eads
1. Basics in threads
What is a thread?
Threads are classi ed according to the main functions they perform in a component.
Primary functions of a thread:
• To form a mechanical coupling
• To transmit motion by converting a rotational movement into a linear movement, and vice
versa.
• To obtain a mechanical advantage, by using a small force to
create a larger force.
Threads are also classi ed into various pro les or forms. The selection of these forms will
be in uenced by many other secondary, but still vital, functions.
Thread forms
The thread pro le de nes the geometry of a thread and includes component diameters
(major, pitch and minor), the thread pro le angle, pitch and helix angle. The most common
thread forms or pro les produced today are shown below.
Application Thread form Thread type
Connecting
General usage
ISO metric, American UN
Pipe threads Whitworth, British Standard (BSPT),
American National, Pipe Threads,
NPT, NPTF
Food and re Round DIN 405
Aerospace MJ, UNJ
Oil and gas API Rounded, API Buttress, VAM
Motion
General usage
Trapezoidal, ACME, Stub ACME