Any of numerous microscopic protein fibres that form part of the cytoskeleton of eukaryote cells. With a diameter of about 10 nm, they are intermediate in size compared to the narrower microfilaments and the wider microtubules—the other main cytoskeletal components. Intermediate filaments are relatively sturdy, forming a three-dimensional mesh within the cell that gives structural support to the nucleus and other cell organelles. Each filament consists of several twisted strands of protein subunits. Intermediate filaments differ in the nature of their protein subunits, often according to the tissue in which the cell is found. For example, those found in protective skin cells consist of keratin subunits and form hair, nails, or wool when the cells die. Those of muscle cells consist of desmin subunits, while filaments in leucocytes are composed of vimentin.