These depth gages is direct reading tools, referencing from their hardened and ground bases.
They are quicker and more convenient to use than any other type of depth gage within their ranges and accuracy.
This gage has a knife-edge base and a needle point contact which has been hardened and ground.
The knife-edge base has a cutout so that the conical point can be precisely positioned for close work.
Point is 1/2″ long with a 60 degree included angle.
In action, the inspector gently pushes the point down to read zero with the base and then pushes down to make the needle point contact the workpiece to take the measurement.