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)
High quality reconditioned original alternatives