High Quality Content by WIKIPEDIA articles! Intermediate filaments (IFs) are a family of related proteins that share common structural and sequence features. Intermediate filaments have an average diameter of 10 nanometers, which is between that of 7 nm actin (microfilaments), and that of 25 nm microtubules, although they were initially designated `intermediate` because their average diameter is between those of narrower microfilaments (actin) and wider myosin filaments. Most types of intermediate filaments are cytoplasmic, but one type, the lamins, are nuclear.