Left Hand Thread VS Right Hand Thread

Left Hand Thread VS Right Hand Thread

The direct a bolt or nut is turned to tighten it determines if it is a left or a right hand thread. Most threads are right hand. Meaning the term Lefty Loosey Righty Tighty is valid.
hand threads
The Left hand thread slopes down to the right , while the Right hand thread does the opposite.

Why use a left hand thread?

Left hand threads are used when there is a chance the nut can come loose because of rotational force. A common example of this is on buffing machines. The buffing machine always turns clock wise , if a right hand thread was used to hold the wheel on the shaft there is a good chance it will come loose. Using a Left hand thread in this application will prevent the nut from coming loose when using the buffer.
buffer