These incandescent "indexed" bulbs have pins are at different heights, so the bulb (and filament) orient in a specific direction within the socket.
This ensures that they meet visibility requirements when used in navigation light fixtures.
• Heavy duty glass envelope for break resistance
• Nickel-plated brass bases prevent corrosion while ensuring a positive point-of-contact
• Filaments, with rough service design, permit hours of reliable burning
• Available in various configurations, tested for dependability
• Sold by the each