The ASTM F1941 specification covers several common electrodeposited coatings on threaded fasteners. The below chart details the various types of coatings, thicknesses, and optional chromates. This ASTM standard replaces ASTM B633 for electrodeposited threaded fastener coatings, since B633 was not written as a fastener specific standard.
F1941 Coating Designations
||Zinc Cobalt Alloy
||Zinc Nickel Alloy
||Zinc Iron Alloy
F1941 Coating Thickness
||Minimum Thickness, in.
F1941 Chromate Finish
||Transparent colorless with slight iridescence
||Transparent with a bluish tinge and slight iridescence
||Olive green, shading to brown or bronze
||Black with slight iridescence
||Any of the above plus organic topcoat
|Note 1 – Coated fasteners with trivalent chromite (Cr+3) are not subjected to the required yellow, opaque and black color.
Note 2 – When fasteners are coated with trivalent chromite (Cr+3) the classification code shall be amended with the letter ‘T’
Coated fasteners heat treated to a specified hardness of 40 HRC or above shall be baked to minimize the risk of hydrogen embrittlement. There is no specified baking duration, exact times and temperatures must be determined between purchaser and manufacturer. If baking is necessary, fasteners must be baked within 4 hours of electroplating. Baking must be performed prior to the application of the chromate finish because temperatures above 150F damage the chromate film. Unless otherwise specified by the purchaser, baking is not mandatory for fasteners with specified maximum hardness below 40 HRC.