This whitemetal casting represents the later pattern Saxby & Farmer signal lamp case. Dimensions are approximately 7½mm high x 5mm wide across the lenses.
This lamp was found on the Lancashire & Yorkshire, Great Eastern, Great Northern and London, Brighton & South Coast railways. It was also used by the London & North Western, until that company started manufacturing its own lamps in the 1880s (see SC0030).
The earlier pattern 3-aspect Saxby & Farmer lamp is SC007.