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How do you visually identify a left from a right thread?


We sometimes speak of left thread and right thread for certain parts, such as steering track rod, nuts, screws, bolts,...
In general, screws and bolts have a right thread. This means that if you hold the screw in one hand and the nut in the other, you turn clockwise to engage the nut on the thread. To unscrew, you turn anti-clockwise.
This is the basic principle.

In some cases, it is useful to have a left thread (also called a reverse thread). This makes it possible to have a distance adjustment (for example for two track rod end on the same bar, 1 left thread and 1 right thread), or to prevent a moving part from unscrewing naturally (threaded water pump axle with viscous coupling).

How do you visually identify a left from a right thread?

You hold the screw/bolt upside down, and draw an imaginary line in the hollow of the thread. You observe which way the imaginary line rises. If it goes up to the right, it's a right thread. If it goes up to the left, it's a left thread.

And that's it, nothing more complicated. :-)

It is very useful to know this information to order the correct steering track rod end, for example.

Exemple :