Car Bulb Fittings: What’s The Difference?

Car bulbs come in all shapes and sizes. Sometimes it can be difficult to determine what bulb fits but it’s also confusing as to why they have different designations.

If you’re wondering what the difference is between different car bulb types or why manufacturers design different bases then you’ve found the right resource centre.

Car Bulb Designations

The bulbs on your vehicle will be designated with a name or number.

For example, your headlight bulbs might be H7 or H4 and your indicators might be 382 or 581.

The suitability of a bulb will often be decided by the team that designed your vehicle.

They might choose that your vehicle uses H7 dipped beam bulbs and H15 main beam bulbs.

It’s something usually out of your control.

Why Do Car Bulbs Have Different Fitting Types?

Essentially, the light output will be the same between the different bulb types but they have different designations due to the amount of voltage and wattage the bulbs will require.

h7 and h4 bulbs example

Why Do My Bulbs Have Different Bases

Manufacturers decided to create different designed bases to prevent drivers from fitting the wrong bulbs and blowing fuses.

Imagine trying to put a square block into a round hole. It’s simple and effective.

How Will I Know My Bulb Type/Fitting?

Remove whatever bulb you need to replace from your vehicle and see if it has any markings of identification tags printed or etched into it.

If not, you could read your vehicle manual or try calling the dealership and if they can’t help, simply email a picture of the bulb to us and we will happily identify it for you.

Related Information

  1. Overview
  2. Why Bulb Bases Are Different
  3. Bulb Base Diagrams


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