The Dollar Project: Sizing Screen
After the coins are minted, a test is performed to make sure the coins are properly sized. The coins are placed in a machine the Mint calls a riddler. A riddler consists of several levels of sizing screens that have holes in them.
The first screen consists of holes that are slightly larger than the actual size of the coin. The screen is shaken and the coins that fall through the holes reach the second level. Coins that do not fall through are too big and are recycled.
The holes in the second sizing screen are slightly smaller than the proper diameter of the coin. Any coins that fall through the holes of this screen are too small and are recycled.