A system of expressing linear density (mass per unit length) of fibres, filaments, slivers, and yarns, or other linear textile material. The basic unit is the tex, which is the mass in grams of one kilometre of the product. Multiples and sub-multiples recommended for use in preference to other possible combinations are:
kilogram per kilometre, designated kilotex (ktex);
decigram per kilometre, designated decitex (dtex);
and milligram per kilometre, designated millitex (mtex).
Tex is a recognized SI unit.
see also count, hank, lea (cotton), flax yarn bundle
Textile Resource (http://www.textile.org.uk)