Term “left handed thread” is often used in cycling literature and practise. This post explains the difference between (a more common) right handed and left handed thread. Before explaining the left handed thread, first the right handed one will be explained.

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1. Right handed thread – “the rule of right thumb”

Right handed thread is made so that bolts and screws are screwed in by turning them clockwise. Unscrewing is, of course, done in the opposite direction. For easier coping (in case of a tricky position, upside down etc.) there is a simple rule of thumb, shown in the picture 1.

The rule of right thumb:When the right thumb is placed onto the head of the screwed in screw (or the hole a screw will be put into), fingers are pointing the direction for tightening the screw.Picture 1

Right handed thread is the most common, while left handed one is exceptional, used only when necessary.

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Threads mentioned in the post about standard bicycle thread dimensions are all right handed.

2. Left handed thread

All the same, but reversed.