Managing humidity is critical to protecting and preserving the condition of your firearms. The Lockdown Hygrometer provides accurate humidity readings at a glance. Excessive moisture in a vault or storage area can cause rapid corrosion and pitting on metal surfaces. It is important to monitor and control the relative humidity in your storage area to be sure your guns are properly protected. Product Details Mounts Easily with included fastener or hook and loop pad Large Easy to Read Numbers 2 3/4 Inch Diameter