One of my biggest pet peeves is 3D printed holes that are not circular or accurate in size. I design a lot of parts that feature pre-formed holes for bolts, rods, and screws, and having to drill these out defeats the purpose of adding them into the model to begin with. I like to use the Nickel Calibration Circle and the Better Nickel Calibration models to test how accurate the printer can print a nickel-sized hole.
While both objects are similar, they each offer unique challenges as one prints a circular object, and the other prints a circular hole that is surrounded by a 90-degree angle and outer arch.
As you can see, the nickel fits nicely into the hole that was printed into the "Better Nickel Calibration" model, and I can confirm that it also fits into the circular print as well. In fact they fit so well that barely any pressure is needed to place the nickel into the hole, and it retains the nickel strong enough to not allow it to fall back out without similar pressure being applied.