What is screw Thread?

Screw thread: screw thread is a combined system a  wire and cylinder , which (wire) attached with a cylinder by twisting position and aggressive .
And it this twisted wire Help the cylinder to move through a fixed measured way!
  This is called screw thread.
Usually a screw threaded bolt use to pair two parts of a machine or elements.
this elements may be metallic or non-metallic.

Kinds: Generally, screw thread is two kinds by bounding system.
They are, 1.With Nut screw bolt 2. without nut screw bolt

1.With Nut screw thread: when two parts of machine have to pair,then use nuted type screw thread. There have  measured hole between two parts whiches are need pair.
The bolt access into the holes and Nut is be wired on Tail of bolt. so, there is become a joint!

2.without nut screw thread: when one part have to pair with another heavy part,then there is use without nut screw.
in main part have a hole with internal thread cutting for screw thread. screw threaded bolt access through auxiliary part's hole and be fixed with heavy part of joint.

Pitch : On a screw thread,One top of thread to another top of another single thread distance parallel measured is called pitch of screw thread.

Root: Down top of screw,when is be pair of two thread is called Root. showed in picture.

Helix: It is the curve traced by a particle, while describing a circular path at a uniform speed and advancing in the axial direction at a uniform rate. In other words, it is the curve traced by a particle while moving along a screw thread

Helix angle: It is the slope or inclination of the thread with the horizontal.
Mathematically,
tan alfa=lead of screw/circumference of screw

Lead: It is the distance, a screw thread advances axially in one turn.

Depth of thread: It is the distance between the top and bottom surfaces of a thread (also known as crest and root of a thread)

Single threaded screw: If the lead of a screw is equal to its pitch, it is known as single threaded screw.

Multi threaded screw:  If more than one thread is cut in one lead distance of a screw, it is known as multi-threaded screw.

by-Engr.shaiful islam majumder
research assistance of mechanical tech