Both the fimbriae and the pili are important protein-filled filaments that originate from the membrane of the bacterial cell and are extended in an outward direction. However, there are differences in the functions and the size of the filaments. For example, when compared to the flagella of the bacterial cells, both of them are shorter. However, the pili tend to have a longer size than the fimbriae. Apart from that, the appearance of the fimbriae is mostly bristle-like while the pili have a hair-like appearance. The pili act as the agents for DNA transfer and fimbriae help in the adhesion of the bacterial cells to the host cells.