Car Bulb Numbers Explained: 1156 vs 1157 vs 3157 vs 7440 and How to Choose
November 12, 2026 · RPS Distributors
A customer walks in with a burnt-out brake light bulb and says "I need the one with two wires." Sound familiar? Small automotive bulbs all look alike at a glance, but the number printed on the base tells you exactly what fits. Get it wrong and the bulb either won't lock into the socket, or it fits but the brake light and tail light don't work the way they should.
This guide is for repair shops, parts counters, fleet techs and DIY drivers who want to understand the most common miniature bulb numbers: 1156, 1157, 3156, 3157, 7440 and 7443, plus how to confirm the right one for a vehicle.
What a bulb number tells you
Miniature bulb numbers are industry trade numbers. They describe the bulb's base, its size and how many filaments it has. Two things matter most when you swap a bulb:
- Base type. Older bulbs like 1156 and 1157 use a metal bayonet base with small pins that twist and lock into the socket. Newer bulbs like 3157 and 7440 use an all-glass wedge base that pushes straight in.
- Single or dual filament. A single-filament bulb has one brightness level. It is used for reverse lights, turn signals or simple marker lights. A dual-filament bulb has a dim filament and a bright filament in one glass, so one bulb can be the tail light (dim) and the brake light or turn signal (bright).
Because the base and filament count are different, these bulbs are generally not interchangeable across families. A 3157 will not fit a 1157 socket, and a single-filament bulb in a dual-filament socket will only light one function.
1156 vs 1157 vs 3157 vs 7440 at a glance
| Bulb | Base | Filaments | Typical uses |
|---|---|---|---|
| 1156 | Metal bayonet, pins level | Single | Reverse lights, turn signals, some trailer lights |
| 1157 | Metal bayonet, pins offset | Dual | Brake/tail, front park/turn on older vehicles and trailers |
| 3156 | Plastic/glass wedge | Single | Reverse lights, turn signals |
| 3157 | Plastic/glass wedge | Dual | Brake/tail, park/turn on many domestic vehicles |
| 7440 | Glass wedge | Single | Turn signals, reverse lights |
| 7443 | Glass wedge | Dual | Brake/tail, park/turn on many import vehicles |
Note the pairs: 1156/1157, 3156/3157 and 7440/7443. In each pair, the first is single filament and the second is dual filament. The 1157 has its locking pins at different heights so it can only go into the socket one way, which keeps the dim and bright filaments connected correctly.
Letter suffixes: A, NA, LL and more
You will often see letters after the number. The base number tells you the fit; the suffix tells you the color or version. Common ones:
- A means amber glass, used where a turn signal sits behind a clear lens (for example 3157A).
- NA means natural amber, another amber-glass version (for example 3057NA or 7443NA).
- LL means long life, a version built for longer service life.
If the vehicle has a clear turn signal lens, it usually needs an amber bulb so the signal shows the right color. If the lens itself is amber, a clear bulb is normally used. Always match what the vehicle maker specifies.
You may also see related numbers like 3057, 4057 and 4157. These are dual-filament wedge bulbs in the same family as the 3157, with different brightness or life ratings. Many vehicles accept more than one of them, but check the owner's manual or a bulb application chart before swapping.
How to find the right bulb for a vehicle
- Read the old bulb. The number is usually stamped on the base or printed on the glass. This is the fastest and most reliable check.
- Check the owner's manual. Most manuals have a bulb chart listing every exterior and interior bulb by position.
- Look at the socket. A metal bayonet socket with two contacts on the bottom is dual filament (1157 style). One contact usually means single filament. A wedge socket has contacts on the sides instead.
- Use a bulb application guide from a bulb manufacturer if the old bulb is missing or unreadable.
Tip for shops: if a customer reports that the brake lights and turn signal act strangely together, check for a single-filament bulb in a dual-filament socket, a bulb installed the wrong way, or a corroded socket before replacing wiring.
Halogen or LED replacement?
LED versions of these bulb numbers are popular. Keep a few points in mind: LED bulbs in turn-signal positions can cause fast flashing on some vehicles because they draw less current, and some vehicles show a bulb-out warning. Color and brightness also have to meet lighting rules for that position. When in doubt, replace with the same type of bulb that came out.
Frequently asked questions
Can I use a 1157 bulb instead of a 1156?
Physically, a 1157 may not lock into a 1156 socket because its pins are offset. Even where it fits, the socket only powers one filament. Use the bulb number the socket is designed for.
Are 3157 and 7443 bulbs the same?
No. Both are dual-filament wedge bulbs, but they have different base sizes and are not designed to swap with each other. Check the old bulb or the owner's manual.
Why do I need an amber bulb if my bulb is the right number?
Some vehicles use a clear lens over the turn signal, so the bulb itself must be amber for the signal to show the correct color. In that case you need the A or NA version of the same number.
Miniature car bulbs we carry
We stock boxes of common miniature bulbs for shops and fleets, including the Heliolite 1156 bulb, the Heliolite 1157 bulb, the Heliolite 3157 bulb and the Heliolite 7440 bulb. Browse more in our bulbs and lighting collection.
Related guides: Headlight Bulb Guide · Truck and Trailer Lighting Checklist
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