The little bumps on the F and J keys
Two keys on your keyboard have a tiny raised ridge or dot. The rest are smooth.
Category: Keys & screens
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Feature. They let your fingers find home without looking.
Touch typists rest their index fingers on F and J. The bumps let them find that home position by feel, then reach every other key from there. The 5 key on a number pad often has one for the same reason.
Source: The reason for bumps on computer keys, Mental Floss.
