The MS3Pro features user-replaceable fuses that protect against voltage spikes and other abuse. To replace these fuses, use a needle nose pliers to pull the fuse out of its holder, and you can push the replacement in with your fingers.
Fuses sold individually. These 500 mA fuses are used in the first generation MS3Pro in the F1 and F2 locations. The MS3Pro EVO uses this fuse in the F4 location (the F5 fuse is a 3000 mA).