Why are there bumps on the F and J keyboard keys?
The small bumps or ridges (homing bars) found on the F and J keyboard keys (position keys) help position your left and right hands without having to look at the keyboard. For example, without looking at your hands, you can feel the small bumps to correctly position your left and right index fingers on the F and J keys. Once your hands are on the home row key position, you can locate the remainder of the keys on the keyboard.
The number 5 on keyboards with a numeric keypad also has a bump to help position your hand on the key pad.