How are the models of crystal diodes named

The model naming of crystal diodes consists of five parts:

The first part represents the main name, and the number "2" represents the diode. The second part represents materials and polarity, represented by letters. The third part represents the category of pipes, indicated by letters. The fourth part represents the serial number, represented by numbers. The fifth part represents specifications, indicated by letters. The meanings represented by the first and third parts of the crystal diode model are shown in Table 1.

The letter meanings of the second and third parts of the diode models shown in Table 1