Fimbriae are small bristle-like solid structures arising from bacterial cell surface. There are 300-400 of fimbriae per cell. Their diameter is 3-10 nm while length is 0.5-1.5 pm. Fimbriae are involved in attaching bacteria to solid surfaces (e.g., rock in water body) or host tissues (e.g., urinary tract in Neisseria gonorrhoeae). Some fimbriae cause agglutination of RBCs. They also help in mutual clinging of bacteria.