If you look at a 220V to 110V wiring diagram, you’ll note that a 220V circuit has two hot wires. That means a 220V plug has to have an extra hot terminal, which is brass by convention. Also by convention, the hot wires are colored black and red. A 110V outlet (and plug) has only one hot terminal, and the hot wire is always black.
Another key difference between 110 and 220 circuits is the wire size. Because 220-volt circuits carry higher current, they require 10 gauge or larger wire, whereas the normal maximum wire size in a 110-volt circuit is 12 gauge. The terminal screws in 220V plugs and outlets are accordingly larger.