This is the lens-reflector unit that fits into the chrome back of a Lucas SLR576 Flamethrower lamp. It will fit perfectly into an original back and it will also fit many reproduction backs. "TOP" appears at the top of the glass; there are no other inscriptions on the unit.
In Related Products below, you can see
BPF bulbs (fog, halogen and yellow bulbs are also available)
Bulb holders
High quality reconditioned original alternatives