Some vehicles use specific bulb holders or locking mechanisms to secure the bulb in the headlight housing. Even when the bulb type is correct (e.g. H7, H1, H4), it may not lock securely without a vehicle-specific holder or adaptor.
This is especially common on BMW, Mercedes, Audi and VW headlight systems, and on newer vehicles where the holder forms part of the headlight mounting. Without the correct holder the bulb may not sit in the right position, affecting beam pattern and light output.
We stock a wide range of vehicle-specific holders and adaptors. If you're unsure, check how your halogen bulb is installed, or contact our support team with photos and we'll help identify the right one.