2n2222 is a bipolar junction transistor with NPN polarity designed to use in general purpose amplification and switching application. The transistor can handle collector current up to 800mA. Its key features are low power, low to medium current, medium voltage, and moderate speed.

2N3904 is a general purpose and very popular NPN Transistor based on Silicon Epitaxial Planar Technology. This NPN transistor finds application in amplification and a simple switching circuit. It comes with a TO-92 package with very less noise. Its pins are compatible with through-hole assembly on PCB.

The A1015 transistors are PNP silicon epitaxial planar transistors. The transistors are well suitable for audio frequency amplifier applications. The transistors measure approx. 0.7 inch long and 0.1 inch wide.