Gage Blocks are one of the most commonly used tools in a Shop or Quality Lab. With too many applications to list, they are simply accurately sized rectangular or square blocks with the ability to be joined together or "wrung" to make a longer working length.  Square blocks have a hole through the middle, which allows them to be clamped together with a rod and jaws while rectangular blocks are wrung together simply by sliding or "wringing" two mating surfaces.

Typically found in a set, Gauge Blocks can be made of steel or ceramic and are available in several grades.  Gage blocks are commonly called: slip blocks or jo blocks (from Johansson gauge).