Car Bulb Fittings: Different Bulb Bases

Bulb Size Information

Understanding why car bulbs are designed differently is one thing but it’s also very important to know what they look like.

We’ve carefully curated a table below designed to show you the base of each of our most popular bulb types and a brief description.

The table will hopefully help you understand the different type of bulb bases available.

Bayonet Type Bulbs

Bulb Designation Description
Designation: 380 Bulb
Filament Type: Double Filament
Pin Type: Offset / Far
Contact Pins: Two
AKA: P21/5W
Designation: 382 Bulb
Filament Type: Single Filament
Pin Type: Inline / Far
Contact Pins: One
AKA: P21W
Designation: 581 Bulb
Filament Type: Single Filament
Pin Type: Inline / Close
Contact Pins: Two
AKA: PY21W
Designation: 566 Bulb
Filament Type: Double Filament
Pin Type: Offset / Close
Contact Pins: Two
AKA: P21/4W
Designation: H6W Bulb
Filament Type: Single Filament
Pin Type: Inline / Close
Contact Pins: One
AKA: 434
Designation: 233 Bulb
Filament Type: Single Filament
Pin Type: Inline / Far
Contact Pins: One
AKA: T4W

Wedge Type Bulbs

Bulb Designation Description
Designation: 501 Bulb
Filament Type: Single Filament
Contact Pins: One
AKA: W5W
Designation: 580 Bulb
Filament Type: Double Filament
Contact Pins: Two
AKA: 7443 or W21/5W
Designation: 582 Bulb
Filament Type: Single Filament
Contact Pins: One
AKA: 7440 W21W
Designation: 955 Bulb
Filament Type: Single Filament
Contact Pins: One (LED’s have 2 for polarity)
AKA: W16W

Headlight Bulbs

Bulb Designation Description
Designation: H1 Bulb
Filament Type: Single Filament
Contact Pins: One
Base Width: 21mm
Designation: H4 Bulb
Filament Type: Double Filament
Contact Pins: Three
Base Width: 43mm
Designation: H7 Bulb
Filament Type: Single Filament
Contact Pins: Two
Base Width: 30mm
Designation: H15 Bulb
Filament Type: Double Filament
Contact Pins: Three
Base Width: 35mm
Designation: HB3 Bulb
Filament Type: Single Filament
Contact Pins: Two
Base Width: 30mm
Designation: HB4 Bulb
Filament Type: Single Filament
Contact Pins: Two
Base Width: 30mm

Related Information

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

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R Shelton
3 years ago

THIS IS BRILLIANT ! (in every sense)

Thank you so much for this EXCELLENT guide on lamp base fittings…it is a much needed clear and detailed description of an otherwise confusing set of codes. To whoever compiled this crystal clear guide – I congratulate you – (someone who actually seems to know what they are talking about, and which therefore gives me some confidence in your companies products !)

Very Helpful !