... % standard:ASTM,DIN,GB ISO9001:2008, ISO14001:2004 black tungsten wire TypePurity of tungsten TypeApplicationWAl1≥99.92TDouble – screwy filament. ... Cathode for emitting tube. High temperature electrodes. Twisted tungsten wire etc.WFolded – heater for electronic tube, etc.WAl2≥ ... for electronic tube. Filament for incandescent lamp. Twisted tungsten wire etc.WFolded – heater for electronic tube, etc.WAl3 ...