An H6W bulb is a 6-watt single-filament bulb on a BAX9s offset-pin bayonet base, used for sidelights, parking lamps, and interior lamps. The H6W carries the UK trade codes 433 and 434, so a box marked 434 holds the same bulb as a box marked H6W. The bulb twists into a small 9-millimetre bayonet holder with offset pins on modern cars, some tractors, and commercial cabs where the parking lamp uses the keyed base. Knowing the H6W by its 6-watt rating and its offset-pin base answers the question behind most H6W searches.
This guide explains what an H6W bulb is, how its BAX9s base fits, why H6W, 433, and 434 name the same bulb family, what the bulb is used for, how it differs from the level-pin T4W, and how to replace one with halogen or LED.
What an H6W Bulb Is
An H6W bulb is a small halogen bulb with one filament on a single-contact bayonet base. The letter H marks the halogen glass, the number 6 gives the 6-watt rating, the W marks the wedge-free bayonet fitting, and the single filament gives one output level, so the H6W suits sidelight and parking duties rather than main lights. The trade number 434 is the figure most British factors print on the box for this bulb.
The H6W produces a bright, steady sidelight from a compact halogen bulb. The 12V H6W runs 6 watts, the offset-pin bayonet base twists into a matching holder, and the single filament switches full on or off, so the H6W lights a sidelight or a parking lamp that needs a small, crisp output. The halogen fill gives the H6W a whiter light than an older tungsten sidelight bulb of the same wattage.
The BAX9s Offset-Pin Bayonet Base
The H6W uses a BAX9s base, a small single-contact bayonet base 9 millimetres across with offset pins. BA marks the bayonet family, the X marks the offset (staggered) pins, the number 9 gives the base diameter in millimetres, and the letter s marks a single contact for one filament. The offset pins sit at different heights, so the bulb drops in one way only and cannot be fitted upside down.
The offset-pin base is the detail that sets the H6W apart. A BAX9s base carries one central contact and two staggered side pins, so it keys into its holder in a single orientation. The BAX9s base differs from the BA9s base used by the T4W, which carries level pins and drops in either way round, so an H6W will not seat in a T4W holder and a T4W will not lock in an H6W holder. The level-pin bulb is covered in T4W (233) bulbs explained, and the wider bulb families in vehicle bulb types explained.
H6W, 433, and 434: One Bulb Family, Close Codes
The H6W name covers the close trade codes 433 and 434. H6W is the descriptive category, a 6-watt halogen bulb on a BAX9s offset-pin base, while 433 and 434 are the trade numbers different factors print for the same bulb, so a buyer asks for any of the three and receives an H6W. The codes and the description point to one bulb family.
- H6W is the descriptive category, a 6-watt halogen bulb on a BAX9s offset-pin base.
- 434 is the common UK trade number for the 12-volt H6W.
- 433 is a close variant code some factors print for the same H6W bulb.
The three labels match one bulb family. A factor stocking 433 or 434 stocks the H6W, and a buyer asking for an H6W receives a 434, so the codes point to the same offset-pin sidelight bulb. A buyer confirms the base is BAX9s, not the level-pin BA9s, before ordering.
What an H6W Bulb Is Used For
An H6W bulb fills a modern sidelight or parking lamp. The 6-watt halogen filament suits four common roles, listed below, which is why the H6W appears across modern cars and some working vehicles.
- Front sidelights and parking lamps on modern cars and commercial cabs.
- Sidelights on tractors and machinery fitted with the keyed BAX9s holder.
- Interior and map lamps that use the offset-pin base.
- Marker and tell-tale lamps on control panels that take the keyed bulb.
The sidelight and parking role defines the bulb. A modern car or a commercial cab runs an H6W in each front sidelight, so a vehicle with a keyed BAX9s holder carries H6W bulbs where an older machine ran a level-pin T4W. The sidelight role across bulb types is covered in position lamps explained, and the reasons a sidelight fails in sidelights not working.
H6W vs T4W: Offset Pins vs Level Pins
The H6W and the T4W both light sidelights and panels, but the H6W uses offset pins on a 6-watt filament and the T4W uses level pins on a 4-watt filament. The two bulbs share the 9-millimetre bayonet family, set out in the table below, so the difference is the pin arrangement and the wattage rather than the base size.
| Bulb | Code | Base | Pins | Wattage |
|---|---|---|---|---|
| H6W | 433 / 434 | BAX9s bayonet | Offset (keyed) | 6W |
| T4W | 233 / 989 | BA9s bayonet | Level (either way) | 4W |
The pins and the wattage are the key differences. An H6W keys into its holder one way and runs a brighter 6-watt halogen filament, while a T4W drops in either way and runs a dimmer 4-watt tungsten filament, so the two are not interchangeable even though both are small bayonet bulbs. A keyed holder takes the H6W, and a level holder takes the T4W. The 4-watt bulb sits in T4W (233) bulbs explained. The larger bayonet bases are covered in BA15s vs BA15d bulb bases.
LED H6W Conversions and Canbus
An LED H6W replaces a halogen H6W in the same BAX9s holder with no rewiring, and the sidelight role makes it a straightforward swap. The LED bulb keeps the offset-pin base, twists into the existing holder, draws a fraction of the 6-watt current, and gives a brighter, whiter sidelight, so it appeals as an upgrade on a modern cab. The convenience is real, though a modern vehicle can flag a warning.
A modern car checks its bulbs by measuring current, so a low-draw LED H6W can trigger a dashboard warning on a canbus system. A canbus-ready LED H6W carries a resistor or a driver that mimics the current of a halogen bulb, so it clears the warning on sensitive vehicles. A tractor or a commercial cab with a simple circuit takes a standard LED H6W without a warning, while a canbus car takes the canbus-ready version. The sidelight marks the vehicle’s width rather than lighting the road, so an LED H6W that keeps the correct colour is a low-risk upgrade, though a road vehicle uses an E-marked LED to stay clear of an MOT query. The wider retrofit rules sit in LED headlamp conversions.
How to Replace an H6W Bulb
Replace an H6W bulb by reaching the lamp, pressing and twisting the offset-pin bulb out, and fitting the new one the correct way round. Five steps cover the job on most lamps, so work through them in order.
- Reach the sidelight, parking, or interior lamp and remove the lens or holder if it clips off.
- Pull the small bayonet holder from the lamp, or reach the bulb directly in a fixed lamp.
- Press the old H6W in, twist it a quarter turn anticlockwise, and lift it out of the bayonet holder.
- Choose a replacement of the correct code (434 or 433 for the H6W), in halogen or a canbus-ready LED, and confirm the base is BAX9s, not the level-pin BA9s.
- Line the offset pins up with the staggered slots, press and twist the bulb clockwise to lock, refit the holder, and test the lamp.
Handle the new bulb by its base to keep the glass clean, because the H6W is a halogen bulb and a fingerprint can shorten its life. The offset pins fit one way only, so the bulb seats correctly when the pins align. For H6W bulbs in halogen and LED, see the bulb range. The level-pin T4W and the larger bayonet bases sit close by, covered in T4W (233) bulbs explained and BA15s vs BA15d bulb bases.
Summary
An H6W bulb is a 6-watt single-filament halogen bulb on a BAX9s offset-pin bayonet base. The H6W runs as the 434 or 433 in 12 volts, used for sidelights, parking lamps, and interior lamps on modern cars and some working vehicles. It differs from the level-pin T4W in pin arrangement and wattage, and from the larger BA15s bulbs in base size. Match the code and confirm the offset-pin base, fit an E-marked canbus-ready LED for road sidelights, and align the staggered pins before locking the bulb home.