This part of JB/T 8950 specifies the model, size, rating, characteristics, bolt-shaped reverse blocking three-pole ordinary thyristor (hereinafter referred to as thyristor) with a rated average on-state current of 5A~400A and symmetrical blocking characteristics. Inspection rules, quality assessment categories, marking, packaging, storage and order forms. This section applies to symmetrical thyristors. Asymmetric thyristors can also be used for reference.