What type of tube is printed with 1D on the patch transistor, what role does it play, and what characteristics does it have?

The MMBTA42 silkscreen 1D amplification factor ranges from 100 to 200. It is a SOT-23 package NPN polarity triode model with high breakdown voltage and low collector emitter saturation voltage. It can be used complementary with MMBTA92(PNP|2D). Don't buy fake goods when you buy.