Final answer:
The POL valve has left-handed threads unique to propane gas cylinders, identified as 0.885" - 14 NGO - LH in the United States, ensuring safe and secure connections.
Step-by-step explanation:
The POL valve, which stands for Prest-O-Lite, is a connection type commonly found on propane gas cylinders. The threads for a POL valve are unique in that they are left-handed, which is opposite to most other types of threads. This means that to tighten a POL connection, you would turn it counterclockwise, and to loosen it, you would turn it clockwise. The specific thread size for a POL valve in the United States is 0.885" - 14 NGO - LH, which stands for National Gas Outlet size 0.885 inches, 14 threads per inch, left-hand thread. This type of threaded connection is designed for safety and to help ensure that the connection of the cylinder to a device is secure and leak-free.