Which tool is commonly used by linemen for safety when climbing poles?

The climbing harness is a vital tool for linemen that enhances safety when climbing poles. This harness is designed to secure the lineman, preventing falls and allowing for safe maneuvering when working at height. It distributes weight evenly across the body and can be quickly attached to a safety line or other secure attachment points to ensure stability and security while working on the pole. Proper use of a climbing harness in conjunction with other safety equipment greatly reduces the risk of injury.

The other options, while important in their own right, do not serve the primary purpose of providing safety during the climbing process itself. Insulated gloves protect against electrical hazards, aerial lift trucks offer a means to elevate workers safely, and protective sunglasses shield against sunlight and debris, but none of these directly aids in securing the lineman to the pole during ascent and descent.