Designed to identify disc brake chambers on commercial trucks that are not measured with other common tools. As with all measurement devices, this tool is designed to narrow your search and all measurements should be confirmed against chamber tags/markings when available. It works best when you push the probe all the way in before placing onto the chamber clamp band. NOTE: This is the first iteration of this product. We are working to cover all Drum and Disc Chambers with one device. ***Mk2 is in active development to cover all chamber sizes***