This halogen bulb will fit older dynamo lights (not LED). Found on many older Dutch bikes. All bulbs are for 6V systems.
2.4W bulbs are for front lights where a rear light is also connected.
3W bulbs are for dynamo systems where there's only a front light.
0.6W bulbs are for rear lights, in a system that also has a front light.
Edison bulbs are screw-in, and plug-in bulbs have a small notch cut into the ring to slot in.