Are 7440 And 7443 Bulbs The Same?

Are 7440 and 7443 bulbs the same? This is a common question for many car owners looking to replace their turn signal bulbs. The short answer is no – 7440 and 7443 bulbs are not identical and serve different purposes. However, there are some key similarities and differences worth understanding when selecting the right bulb for your vehicle lighting needs.

When replacing turn signal bulbs on your vehicle, it’s important to select the correct bulb type to avoid compatibility issues. 7440 and 7443 bulbs may look similar, but have different bases, filaments, brightness levels and applications. While a 7443 bulb can sometimes be used to replace a 7440, the reverse is not true. Let’s take a deeper look at how these two popular auto bulb types compare.

Filament Differences Between 7440 and 7443 Bulbs

One of the biggest differences between 7440 and 7443 bulbs comes down to the filament design.

7440 Single Filament

The 7440 bulb has a single filament and one contact point on the base. This makes it well-suited for simple on/off applications like rear turn signals. The single filament gives a crisp, solid light when illuminated.

7443 Dual Filament

In contrast, the 7443 utilizes a dual filament design with two separate contact points. This enables the bulb to handle more complex wiring applications. One filament powers the parking or tail light function, while the other controls the turn signal. This provides added visibility and safety benefits.

The dual-filament construction also allows the 7443 to produce a brighter, more vibrant turn signal indicator. This makes it an ideal choice for front turn signals.

Base Types – Bayonet vs Wedge

7440 and 7443 bulbs also use different base configurations to connect to the vehicle socket.

7440 Bayonet Base

The 7440 turn signal bulb uses a simple bayonet-style base. Two small tabs insert into gaps in the socket, allowing the bulb to twist into place. This creates a reliable connection. Bayonet bases are common for rear lamp bulbs.

7443 Wedge Base

The 7443 wedge base has a different shape with no locking tabs. The wedge design simply slides straight into the housing until tight. This self-securing fit works well for front bulbs that require more vibration resistance.

So the 7443 wedge base provides a tighter, more durable connection than the bayonet style 7440.

Brightness and Applications

The dual-filament 7443 bulb produces a noticeably brighter light output than the single-filament 7440. Here are some typical uses:

  1. 7440 bulbs – Rear turn signals, brake lights, reversing lights
  2. 7443 bulbs – Front turn signals, parking lights, marker lights

So in most vehicles, 7443 bulbs are used for the front lighting while 7440 bulbs are fitted in the rear. This takes advantage of the 7443’s extra brightness where it’s most needed.

Can You Use a 7443 Instead of a 7440 Bulb?

This is a common question for those looking to replace 7440 rear turn signal bulbs. In most cases, the 7443 can substitute for a 7440 – but not the other way around.

Here’s why the 7443 works as a 7440 replacement:

  1. The 7443 wedge base can fit into a 7440’s bayonet socket.
  2. The extra 7443 filament simply won’t connect, so only one filament will light.
  3. This allows it to function just like a 7440, but with added brightness.

So using a 7443 bulb to replace a 7440 is possible with no modifications or issues. Just be aware the extra filament will remain unconnected.

Can a 7440 Replace a 7443 Bulb?

Unfortunately, a 7440 cannot directly replace a 7443. Here are the challenges:

  1. The 7440 bayonet base is incompatible with the 7443 wedge socket.
  2. Even if adapted, the 7440 single filament can’t power both parking and turn functions.
  3. This would result in loss of lights or other wiring problems.

For these reasons, you should always replace a 7443 bulb with another 7443. Purchasing the identical replacement will avoid any installation or performance problems.

How to Tell 7440 and 7443 Bulbs Apart?

7440 and 7443 bulbs can look very similar at first glance. Here are a few easy ways to visually distinguish them:

  1. Filaments – The 7443 will have two visible filaments, while the 7440 has just one.
  2. Base – The 7443 has a wedge base and the 7440 is bayonet style.
  3. Part number – Printed markings with the bulb type (7440 vs 7443) are usually on the base.
  4. Packaging – The bulb type will always be printed on the packaging or product description.

Checking for the two-filament 7443 or single-filament 7440 is the quickest way to identify the bulb type if you have it in hand. But when purchasing replacements, always go by the printed bulb number to guarantee compatibility.

Bulb Sizes: T20 vs 168

You may also see 7440 and 7443 bulbs specified by another sizing system which refers to the bulb glass diameter in millimeters. Here’s how these measurements compare:

  1. 7440 bulbs are often marked as T20 size, indicating 20mm diameter.
  2. 7443 bulbs will typically be listed as 168 size, or 16.8mm diameter.

So a 7443 168 bulb is slightly smaller in diameter than a 7440 T20. But in practice, the filament design and base type are more important than the overall glass size when determining compatibility.

Choosing the Right Bulb Type

When shopping for replacements, the key is matching your existing bulb’s fit and performance:

  1. For rear turn signals on most vehicles, look for a 7440 single-filament bayonet bulb.
  2. For front turn signals that are brighter, search for a 7443 dual-filament wedge bulb.

Some higher-end LED replacement bulbs are designed to support both configurations. But always double check which bulb style your vehicle uses before purchasing.


To recap, 7440 and 7443 bulbs have distinct designs making them suited for different applications:

  1. 7440 bulbs use single filaments and bayonet bases, best for rear lights.
  2. 7443 bulbs have dual filaments and wedge bases for front signals.

While a 7443 can sometimes substitute for a 7440, the reverse swap doesn’t work. Matching your existing bulb style exactly will ensure fast, trouble-free installation. Knowing the differences between these popular auto bulb designs will save you time and headaches down the road.

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Ammar Masoud

I have had a long and fulfilling career in the automotive industry, primarily with Honda and Acura. With 15 years of experience as a Honda service technician, I became highly skilled in repair and maintenance, gaining a deep understanding of these vehicles. After many years in the automotive field, I decided to embark on a second career in industrial manufacturing. It was a significant change, but I found that the skills I had honed in the automotive industry were incredibly valuable in my new role. In my current position in industrial manufacturing, the demand for quality workmanship and meticulous attention to detail is paramount. Fortunately, these are traits that I have cultivated throughout my years in the automotive industry. I take pride in applying these skills to meet the high standards expected in the manufacturing sector.