Short answer: look at the lens material and the head construction. Glass lens with a sealed beam means 325. Polycarbonate lens on an ABS head means 330. High-impact PC/ABS with a vent means 335 or X335. Everything you need to order the right lamp follows from that.
The four Unity heads at a glance
| Series | Head | Lens | Tell |
|---|---|---|---|
| 325 | 6 in S04, ABS, black | Glass | Sealed beam behind glass, front ring |
| 330 | 6 in high intensity, ABS | Polycarbonate + UV inhibitor | H3 bulb, sharper beam, front ring |
| 335 | 6 in S04, PC/ABS | Hard-coated polycarbonate | PAR46 LED, anodised aluminium reflector |
| X335 | 6 in composite, PC/ABS | Hard-coated, replaceable | GORE-TEX vent, nickel-plated zinc heat sink |
What does S04 mean?
S04 is Unity's designation for the 6-inch head casting used across the 325 and 335 families and on most of the vehicle-specific part numbers such as 218010-0002 and 219070-0002. It is a head style, not an output rating — two S04 spotlights can carry a 50-watt or a 100-watt lamp. So the head marking narrows the family; the lamp inside sets the output.
How do I read the shaft code?
On assemblies sold by series, the letters after the number are the shaft: 330GM is a 330 head on a GM shaft, 330V on a V shaft. Unity uses nine codes — A, CL, DC, GM, H, O, P, PL and V — and each matches a particular pillar geometry. Vehicle-specific part numbers such as 205040-0002 do not carry a letter, because the shaft is implied by the vehicle.
What if the head has no markings at all?
Measure and look. A glass lens rules out everything but the 325. A vent on the back of the head means X335. If the lamp is a screw-in H3 bulb, it is a 330. Failing that, the fitment search will narrow it from the vehicle: most bodies only ever took one or two combinations.
Why does identifying it matter?
Because the service parts differ. A 330 lens will not fit a 325, the 335 and X335 are lamp assemblies rather than re-lampable heads, and the handle you need depends on shaft length rather than on the head at all. Getting the series right first makes every subsequent order straightforward.
