These towers can be used to measure the diameter of O-rings, eliminating the need for calipers/rulers. Simply put the O-ring around the tower until it fits snug and count the rungs down. I tried designing the measurements into the tower, but it is more effective to use a small marker to mark the increments.

Big = 61mm-100mm diameter

Small = 3mm-60mm diameter

Tallest tower is 240mm (small.stl), but you can stop the print early if you don't need it for small O-rings