GMNA GM6138M PDF

This specification covers requirements for a corrosion resistant black finish over an electroplated zinc-nickel alloy substrate. This coating is intended primarily for bulk processed small steel parts such as bolts, screws and nuts used on exterior visible parts. This coating is especially suitable for internal drive (cross recess, torx, etc.) threaded fasteners and self drilling and tapping screws.

Material Description. At present the approved suppliers of this specification provide coatings with hexavalent chromate and some without hexavalent chromate. Effective July 2005, only sources with hexavalent chromate free system shall be in the MATSPC database, approved source list. All Chemical Suppliers/Applicators currently in the MATSPC database approved source list, who are providing hexavalent chromate free coating shall submit the name of the chemicals currently used and a signed certificate that their coating system is free of hexavalent chromate, with no hexavalent chromate in the final product per GMW3059 requirements. GMW3034 will be used as a referee test.

This coating is scheduled for deletion. Don't use this coating on new designs. GMW4205 is recommended for new designs.

Use of this finish on threaded surface and/or bearing surface of joints could affect the torque-tension relationship. It is recommended that a torque-tension study of the fastener joint be performed before releasing this new finish on a new application.