Lead is the axial advance of a helix or screw during one complete turn (360°) The lead for a

screw thread A screw thread, often shortened to thread, is a helical structure used to convert between rotational and linear movement or force. A screw thread is a ridge wrapped around a cylinder or cone in the form of a helix, with the former being called a ...

is the axial travel for a single revolution. ''Pitch'' is defined as the axial distance between adjacent threads on a helix or screw. In most screws, called "''single start''" screws, which have a single helical thread along their length, the lead and pitch are equal. They only differ in "''multiple start''" screws, which have several intertwined threads. In these screws, the lead is equal to the pitch multiplied by the number of "''starts''". Lead angle is the angle between the helix and a plane of rotation. It is the complement of the

helix angle In mechanical engineering, a helix angle is the angle between any helix and an axial line on its right, circular cylinder or cone. Common applications are screws, helical gears, and worm gears. The helix angle references the axis of the cylinder, ...

, and is used for convenience in worms and hobs. It is understood to be at the

standard pitch diameter This page lists the standard US nomenclature used in the description of mechanical gear construction and function, together with definitions of the terms. The terminology was established by the American Gear Manufacturers Association (AGMA), under ...

unless otherwise specified. The lead angle can be expressed as: :

\mbox = \arctan \left( \frac   \right)

where :''l'' is lead of the helix :''d_m'' is mean diameter of the helix In American literature ''λ'' is used to notate the Lead Angle.Juvinall & Marshek. Fundamentals of machine component design. John Wiley & Sons Asia: 2006. Page 391. In European literature, ''Υ'' (Greek letter gamma) may be used.

Notes

{{reflist Gears Screws Metalworking terminology de:Gewinde#Gewinde-Kenngrößen

See also

Notes