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.