T-1 1/4 (4mm) Subminiature Incandescent LampsT-1 & 1/4 Lamps have a nominal diameter of 0.160 inches (4,1 mm) Subminiature Lamps T-1 ¼ Wire Terminal T-1 ¼ Midget Flange T-1 ¼ Knurled Screw T-1 ¼ Bi-Pin