AS NZS 1214:2016 pdf download.Hot-dip galvanized coatings on threaded fasteners (ISO metric coarse thread series) (ISO 10684:2004, MOD).
5.6 Spinning and quenching
Parts shall be spun immediately following removal from the galvanizing bath and quenched in water or air cooled depending on size consideration.
5.7 Special requirements for nuts
Nut threads and other internal threads shall be tapped after hot dip galvanizing. Retapping shall not be
permitted.
5.8 Post-treatment
Most galvanized parts do not require any post treatment. When required by the purchaser, treatments such as chromating or phosphating may be applied to reduce the possibility of wet storage staining (white corrosion) or to assist subsequent painting.
6 Requirements on thread tolerances and additional marking
6.1 General
Dimensional limits for ISO metric screw threads M10 to M64 before and after coating are specified in
ISO 965-1 to ISO 965-5. All other dimensions and tolerances of fasteners apply before hot dip galvanizing.
Dimensional limits for internal and external screw threads M8 with thread tolerances 6AX and 6AZ for internal
threads and 6az for external threads are specified in Annex B.
NOTE It is not possible to check the thread tolerance of a hot dip galvanized part by stripping the coating and gauging the thread thereafter, since some steel is dissolved from the part during the galvanizing process.
6.2 Requirements and precautions in assembling hot dip galvanized threaded fasteners
6.2.1 General
This clause applies only to parts with thread tolerances in accordance with ISO 965-1 to ISO 965-5 and with marking according to the marking requirements for fasteners as given in ISO 898-1 and ISO 898-2. The marking specified in 6.2.2 and 6.2.3 shall be carried out in addition to the marking according to ISO 898-1 and ISO 898-2.
The application of zinc coating by the hot dip process results in the deposition of a heavy coating thickness of zinc (always in excess of 40 pm). Hence, it is necessary to manufacture screw threads to special limits in order to accommodate such heavy coatings.
There are two different methods provided for, which give the necessary fundamental deviations (clearances) for the zinc layer applied to fasteners by hot dip galvanizing.
The first method (see 6.2.2) consists of using nuts tapped oversize to tolerance class 6AZ or 6AX after coating, to mate with bolts or screws manufactured with screw threads to tolerance position g or h before coating.
The second method (see 6.2.3) consists of using bolts or screws manufactured with threads undersized to tolerance class 6az before coating, to mate with nuts tapped to tolerance position H or G after coating.
Nuts tapped oversize (marked with Z or X) shall never be mated with bolts or screws with undersized threads (marked with U), because such combinations create a high probability of thread stripping.
Assembling hot dip galvanized nuts tapped to tolerance position H or G after coating with hot dip galvanized bolts or screws manufactured with threads to tolerance position g or h before coating results in thread interference.AS NZS 1214 pdf download.