Left-hand thread – Thread is not equal to thread

The left-hand thread
Thread is not equal to thread

Left-handed threads or also left-turning or left-rising threads are those which can be screwed together counterclockwise. These are marked with the abbreviation LH.
LH here stands for left-handed or “left hand”.

With this type of thread it should be avoided that the thread loosens by itself. This is the case with the left-hand bicycle pedal, for example.

In addition, the left-hand thread is often used as a safety lock for gas bottles to prevent life-threatening mix-ups.

Nahaufnahme von Gewindeschneider und Schneideisen: An der Beschriftung LH lässt sich das Linksgewinde erkennen

Left-hand thread: Hanging tap


Cutting left-hand threads

Cutting the internal thread for left-hand threads

Cutting left-handed threads is identical in sequence to making right-handed threads. The decisive difference lies in the direction of rotation of the tool.

For left-handed threads, the lead of the tap tip has a shape ground to the right.

Taps and dies for left-hand threads


Cutting the external thread for left-hand threads

The same applies to the cutting of the external thread for left-hand threads. There are special dies for the production of left-handed threads.

Schneideisen für Linksgewinde: Schneidzähne haben einen anderen Anschnitt. Auf der Beschriftung am Schneideisen ist das Kürzel LH (Linksgewinde)

Die for left-hand thread


Otherwise, the information on thread size and dimension remain the same.

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