Lead is the axial advance of a

helix A helix () is a shape like a corkscrew or spiral staircase. It is a type of smooth space curve with tangent lines at a constant angle to a fixed axis. Helices are important in biology, as the DNA molecule is formed as two intertwined helic ...

screw A screw and a bolt (see '' Differentiation between bolt and screw'' below) are similar types of fastener typically made of metal and characterized by a helical ridge, called a ''male thread'' (external thread). Screws and bolts are used to ...

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 ...

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 In geometry, a plane of rotation is an abstract object used to describe or visualize rotations in space. In three dimensions it is an alternative to the axis of rotation, but unlike the axis of rotation it can be used in other dimensions, such as ...

. It is the complement of the helix angle, 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