The Lucas 1130 lamp definitely has threads for two bolts as mentioned so either the rear bolt is missing or the factory have only drilled one hole, the one that goes through the wing stay. Less holes less corrosion i guess?
On my car the bolt(s) are also the earth, some cars may use an earth wire which is probably better.
I tried the led bulbs but they are bright white and make the headlights look distinctly yellow, so reverted to originals.
