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The CNC Tool holders are highly precision products, used for high precision machines and automotive application, in these tool holders the shank is a very close tolerance component made from spheroidal graphite cast iron and it needs dimensional accuracy during assembly. Blackening process is involved to maintain aesthetic and anti-rusting properties, a huge rejection, colour variation and heavy distortion are constraints in blackening. Blackening is conducted with new imported chemical salt for minimising the distortion and achieve good black colour finish with various process parameters with relative combinations of temperature, time, and bath strength to set suitable appropriate process parameters and study the salt formula ratio. Salt spray fuming test conducted for anti-rust study and dimensions are verified with CMM and other precision instruments to study the dimensional accuracy. Manganese Phosphate process also added at 80° C to improve the aesthetic and the cast iron blackening optimized the less distortion at 120° C for 20 minutes dipping time in the chemical ratio of 1:3 combination. A study of salt analysation also will be carried out to ensure the alkaline base chemical ratio presented in the commercial salt and the cold blackening combination is the further study in this same research as continual improvement study. [ABSTRACT FROM AUTHOR]