thread

A thread is a technical element of machine parts, the shape of which is defined by the threaded surface. The surface is created by winding the profile on a cylinder along a helix at a defined pitch.

The thread can be:

Right (regular)
Left
Internal (nut)
External (screw)
One-way
Multiple
Cut
Formed (rolled)
Nomenclature
Thread surface - the surface created by the movement of the thread profile so that each of its points describes a helix, while the axial displacement per revolution is equal to the perpendicular projection of the thread profile to the axis, or a multiple of this length by an integer.
Helix - the line created by a point while rotating uniformly around a fixed axis and at the same time moving uniformly in its direction.
Thread profile - an imaginary curve (broken line) that is bounded by two equidistant points lying parallel to the axis of the thread. Its tops are usually beveled or rounded.

Division of threads according to profile and pitch
Metric thread (M), apex angle 60°

• • Fine metric thread
    Whitworth thread (W), apex angle 55°, dimensions given in inches, introduced by Whitworth 1841
    Whitworth thread with top clearance
    Pipe thread (G), apex angle 55°, dimensions in inches, used by plumbers
    Conical pipe thread (G kon), (introduced by Whitworth 1841)
    Round thread (Rd), used e.g. for connecting rods of wagons
    Edison thread (E), used e.g. with light bulbs
    Trapezoidal thread isosceles (Tr) apex angle 30° (in the USA 29°) or trapezoidal, used in machine tools
    Trapezoidal thread unequal arm (S)
    Armor thread (Pg), apex angle 80°, used for cable glands
    Flat thread - the cross section of the thread is a square
    Loewenherz thread - apex angle 53°8' - used in Germany in the 19th century, the apex angle corresponds to an equilateral triangle with a height equal to the base.
    Sellers thread - used until the beginning of the 20th century in the USA
    American coarse thread (introduced 1922)
    ASME American fine thread - (introduced 1907)