Handedness Screw thread

right- , left-handed screw threads



the right-hand rule of screw threads

the helix of thread can twist in 2 possible directions, known handedness. threads oriented threaded item, when seen point of view on axis through center of helix, moves away viewer when turned in clockwise direction, , moves towards viewer when turned counterclockwise. known right-handed (rh) thread, because follows right hand grip rule. threads oriented in opposite direction known left-handed (lh).

by common convention, right-handedness default handedness screw threads. therefore, threaded parts , fasteners have right-handed threads. left-handed thread applications include:

where rotation of shaft cause conventional right-handed nut loosen rather tighten due applied torque or fretting induced precession. examples include:

the left hand pedal on bicycle.
the left-hand grinding wheel on bench grinder.
the lug nuts on left side of automobiles.
the securing nut on circular saw blades - large torque @ startup should tend tighten nut.
the spindle on brushcutter , line trimmer heads, torque tends tighten rather loosen connection


in combination right-hand threads in turnbuckles , clamping studs.
in gas supply connections prevent dangerous misconnections, example:

in gas welding flammable gas supply uses left-handed threads, while oxygen supply if there 1 has conventional thread
the pol valve lpg cylinders


in situation neither threaded pipe end can rotated tighten or loosen joint (e.g. in traditional heating pipes running through multiple rooms in building). in such case, coupling have 1 right-handed , 1 left-handed thread.
in instances, example ballpoint pens, provide secret method of disassembly.
in mechanisms give more intuitive action as:

the leadscrew of cross slide of lathe cause cross slide move away operator when leadscrew turned clockwise.
the depth of cut screw of stanley type metal plane (tool) blade move in direction of regulating right hand finger.


some edison base lamps , fittings (such formerly used on new york city subway) have left-hand thread deter theft, since cannot used in other light fixtures.




^ brown, sheldon. bicycle glossary: pedal . sheldon brown. retrieved 2010-10-19. 
^ http://www.directindustry.com/prod/s-w-manufacturing-co-inc/clamping-studs-57807-574221.html