Editing Screw thread (section)

====Coarse versus fine====
Coarse threads are those with larger pitch (fewer threads per axial distance), and fine threads are those with smaller pitch (more threads per axial distance). Coarse threads have a larger threadform relative to screw diameter, where fine threads have a smaller threadform relative to screw diameter. This distinction is analogous to that between coarse teeth and fine teeth on a [[saw]] or [[File (tool)|file]], or between coarse grit and fine grit on [[sandpaper]].

[[File:XK engine camshaft cover front stud-0822.jpg |thumb|Camshaft cover stud threaded {{frac|1|4}}-20 UNC (left, for aluminium cylinder head) and {{frac|1|4}}-28 UNF (right, for steel nut; from a 1960s [[Jaguar XK6 engine|Jaguar XK engine]])]]
The common V-thread standards ([[ISO 261]] and [[Unified Thread Standard]]) include a coarse pitch and a fine pitch for each major diameter. For example, {{frac|1|2}}-13 belongs to the UNC series (Unified National Coarse) and {{frac|1|2}}-20 belongs to the UNF series (Unified National Fine). Similarly, M10 (10&nbsp;mm nominal outer diameter) as per ISO 261 has a coarse thread version at 1.5&nbsp;mm pitch and a fine thread version at 1.25&nbsp;mm pitch.

The term ''coarse'' here does not mean lower quality, nor does the term ''fine'' imply higher quality. The terms when used in reference to screw thread pitch have nothing to do with the tolerances used (degree of precision) or the amount of craftsmanship, quality, or cost. They simply refer to the size of the threads relative to the screw diameter.

Coarse threads are more resistant to stripping and cross threading because they have greater flank engagement. Coarse threads install much faster as they require fewer turns per unit length. Finer threads are stronger as they have a larger stress area for the same diameter thread. Fine threads are less likely to vibrate loose as they have a smaller helix angle and allow finer adjustment. Finer threads develop greater preload with less tightening torque.<ref name=katonet>{{cite web |title=Coarse Threads vs. Fine Threads |website=katonet.com |url=http://www.katonet.com/article/coarsevsfine.html}}</ref>