In 2mm glass. It would have originated from a BR fogmans lamp & 4 are needed to complete one aspect of a three aspect lamp OR 3 needed for a 4 aspect lamp.
Antique British Railway Hand Lamp – Welch Patent – Lamp Mfg London
Antique British Railway Hand Lamp – Lamp Mfg London
Vintage British Railway Hand Lamp Lantern
BRITISH RAILWAY HAND LAMP GLASS 4.75 IN DIA 6MM THICK BEVELLED EDGE & BEZEL (B)
ONE BRITISH RAILWAY HAND LAMP BLUE GLASS SLAT C 1950 BR 12cm x 2.2cm 3 AVAIL
BRITISH RAILWAY HAND LAMP GLASS 3.50 IN DIA 3MM THICK BEVELLED EDGE VGC