Thread style refers to the
direction of twist of the threads on a threaded fastener.
- Right hand threads
follow the right hand rule. If the fastener is held as if it were to be
inserted into a tapped hole, nut, etc., turning it clockwise would
tighten it. This can be represented by holding a hand with the fingers
curled and the thumb extended, and rotating the hand towards its own
fingertips, rather like the action of a screwdriver driving a screw.
- Left hand threads follow the
left hand rule, which is the opposite of the right hand rule. In this
case, the left hand threaded fastener would loosen if it was turned
clockwise. This is useful in situations where normal use would actually
loosen the fastener, such as on the left hand pedal of a bicycle, or the
nut on a circular saw blade.
- Right and
left hand threads refer to a threaded fastener that has both
right and left hand threads, on opposite ends of the fastener. This can
occur in such items as threaded rods and studs, and in the interior
threaded portion of a turnbuckle.