Double Ended Bowl Calipers

Double Ended Caliper. 

Typically these are used for measuring the thickness of bowls or other lathe projects but can really be used to measure anything you want. Allows you to get the thickness of items and object in areas traditional calipers can't reach by measuring the opening on opposite end of the caliper. 

Print the part twice and lay them on top of each other using a M5 bolt to hold it together (I use a nylon lock nut so i can adjust the friction to what i like)