F1 terminals are 3/16 (0.187) inches wide. They fit into the corresponding F1 connectors at the end of the wire leads for the device they're powering.
F2 terminals are 1/4 (0.25) inches wide -- about 1/16 of an inch wider than the F1. They fit into the corresponding F2 connectors on the wire leads that connect to the particular device they're powering.
There are also adapters available that can make the F1 terminal compatible with an F2 connectors, and vise versa.
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