K index: (1) Index in general is used for characterizing a commercial grade of polyvinylchloride, calculated from its viscosity in solution and indicating its molecular weight. Polyvinylchloride with a K value of approximately 6880 is usually used for coating. (2) Index is used for the classification of basic (cationic) dyes with respect to their rate of strike (Association index K). (3) Index is used in association with machines for measuring fabric length because of the effect on standardized length measurement due to the stretching of the material.