Pilus

A pilus (Latin for 'hair'; plural : pili) is a hairlike appendage found on the surface of many bacteria. The terms pilus and fimbria (Latin for 'thread' or 'fiber'; plural: fimbriae) can be used interchangeably, although some researchers reserve the term pilus for the appendage required for bacterial conjugation. All pili are primarily composed of oligomeric pilin proteins.