What Makes Left Hand Thread Fasteners Unique?

What is a left-hand threaded fastener?

A fastener catalog that sells UN (SAE) shows a fastener with these specifications: 0.250 x 20 UNC - 2A-LH. What is unique or unusual about this fastener?

Answer:

The fastener's specifications 0.250 x 20 UNC - 2A-LH refer to its diameter, threads per inch, type of threading, class of fit, and direction of threading. The 'LH' at its end makes it unique as it indicates a left-hand threading, unlike most fasteners that have a right-hand threading.

Left-hand threaded fasteners are designed with threads that tighten when turned counterclockwise and loosen when turned clockwise, which is opposite to the operation of right-hand threaded fasteners. This unique feature makes them suitable for specific applications where regular fasteners may unscrew themselves under certain conditions.

The notation 0.250 x 20 UNC - 2A-LH in the fastener catalog refers to the specifications of a Unified National Coarse (UNC) fastener. '0.250' indicates the diameter in inches, '20' represents the threads per inch, 'UNC' stands for Unified National Coarse threading, and '2A' signifies the class of fit.

Left-hand threaded fasteners are less common than right-hand threaded ones but can be essential in situations where their unique tightening direction is advantageous.