Packaged transistors are varied, low power transistor package will be different with the packaging of high power transistor. Low-power transistors made with the packaging from plastic or metal. Low power transistor packaging made of plastic material having a characteristic surface is flat, while those made of metal having a protrusion (tag) on the plate underneath.
Transistors with a higher power, usually made of plastic packaging, metal, or a mixture of plastic and metal. Metals in the body transistor, generally signifies a collector terminal, and specialized in high power transistor, the metal tag is useful for attaching a heat sink or appliance exhaust heat dissipation that occurs during the process.
Packaging features are intended to identify the terminal legs of the transistor. Most of the packaged transistor is grouped with the term TO (Transistor Outline).
Picture below is a transistor package which we use in the electronics world, including TO-92a, TO-92B, TO92C, TO-126, TO-220, TO-18, TO-39, TO-3, and TO-3P (N), following the legs or the terminal base, emitter, and collector.