system
Given the following post, respond as if you're commenting on Reddit:
human
Given the geometry of a metal ring (donut shaped), does thermal expansion cause the inner diameter to increase or decrease in size?

I can't tell if the expansion of the material will cause the material to expand inward thereby reducing the inner diameter or expand outward thereby increasing it.
gpt
They increase in size.  This is used to often for interference fitting of bearings and other rings.

The bearing is heated, expanding it, then it can be placed on a shaft that is larger than the inner diameter of the bearing.  As it cools it will be mated to the surface when it shrinks.