 
  
  
                | Trade mark | Added impurity | Impurity quantity % | Other impurity | Electric discharged power | Color sign | 
| WZ3 | ZrO2 | 0.20~0.40% | <0.2% | 2.5~3.0 | brown | 
| WZ8 | ZrO2 | 0.70~0.90% | <0.2% | 2.5~3.0 | white |