The Monument 2065F is a radiator valve spanner used to hold a radiator valve in place while you tighten or loosen the valve nut. To use it, place the plastic spanner on the valve to hold it steady, and use another tool to turn the nut. This prevents the valve from rotating and protects the finish, facilitating the installation or removal of standard and thermostatic radiator valves. 
Step-by-step guide
Identify the valve: Find the radiator valve you need to work on. The Monument 2065F is designed for both standard and thermostatic radiator valves.
Position the spanner: Place the plastic-faced Monument 2065F spanner onto the valve's body to hold it steady. This prevents it from turning when you apply force to the nut.
Use a second tool to turn the nut: Use another appropriate tool, like a wrench or water pump plier, to turn the nut you need to adjust.
Tighten or loosen: Turn the nut in the desired direction. The 2065F will hold the valve stationary, allowing you to tighten or loosen the nut without the whole valve twisting.
Complete the task: Once the nut is at the desired tightness or looseness, remove both the spanner and the second tool. The 2065F's plastic construction helps prevent damage to the valve's finish.