What is the primary function of a lug spanner?

The primary function of a lug spanner is to remove lug nuts and bolts. This tool is specifically designed to provide the necessary torque to loosen or tighten the nuts that hold a vehicle's wheel in place. By having a handle and a socket that fits over the lug nuts, a lug spanner enables the user to apply sufficient force during wheel changes or maintenance. This is particularly useful in emergency situations, such as a flat tire, where quick and efficient removal of the wheel is required.

The other options refer to different tools or functions that are unrelated to the purpose of a lug spanner. Inflating tires, measuring tire pressure, and applying brake pressure require different equipment specifically designed for those tasks, highlighting the unique role of the lug spanner in vehicle maintenance as a tool focused on wheel assembly.