These #259 bulbs replace #555 bulbs in high-vibration areas such as pop bumbers and playfield locations that suffer shock from ball strikes or local mechanisms. For example, the "F" light by Creature's left flipper. Also, put them in pop bumpers that are difficult to access because of ramps and plastics - you will not have to change them so often!
They have a thicker filament than a 555, which makes them stronger. They are also a shade dimmer, although they take the same power. You won't notice.
(Note: if you pop bumper bulb touches the bumper body, not much will save it from an early failure. Use the leads as a spring to keep the bulbs away from the body).