A standard Caliper with integrated measuring bridge, but without measuring blades is called depth caliper.
It can be used to measure the depth of holes (which don’t pass through) or grooves.
Function and design are almost identical to the standard caliper.
With mechanical depth calipers, the determined measurement is read off via the vernier.
For the digital version the value can be seen on the display.
Picture: Measuring Technology: Depth Caliper (analog and digital) for measuring depth of holes or grooves.
Measuring Technology: Depth Caliper