T 0005 (OTTO) Tantalum wire, 0.5 mm (0.02 in) dia, 99.95% Cas 7440-25-7 - used for light bulb filaments until tungsten replaced it in widespread use. T 0005 (OTTO) Tantalum wire, 0.5 mm (0.02 in) dia, 99.95% Cas 7440-25-7 - used to produce a variety of alloys that have high melting points, are strong and have good ductility.