Here is my big size thickness caliper, for measuring the thickness of the walls of a woodturned vessel for example.
With this kind of caliper, you need to hold the tool in place on one side, while measuring or simply appreciating the thickness displayed on the other side.
I have made an optional branch more flat, to be used for narrow vessel necks, whereas the two rounded branches will be more suitable for measuring the bottom of a bowl for instance.
The cross is made of flat steel, the bended parts are made of square steel.
Overal length is about 50 cm.