Allison writes: Ethan asks: ? What is different about the metal can and the plastic case part? Mostly lead spacing and cosmetics. Metal can pinouts are in a semicircle, the TO92 is a straight line layout. If the original was a metal can soldered down flat to the PCB, chances are the plastic transistor will be showing some leg if used as a replacement. Metal cans can be heat sinked better than a plastic part obviously, and for peripheral or line drivers heat dissipation may be important. For a while in the 60's and 70's, the metal can parts had superior hermetic seals that were important in some space and mil-spec applications, but since then the plastic packages have been entirely perfected. Tim.