Due to their small relative size, threaded fasteners, nuts and washers are usually hot dip galvanized via the centrifuge process.
Like other moving parts, each part needs to be galvanized separately.
- The HDG process develops a coating of a minimum average thickness of 50µm on threads, as defined in AS/NZS 1214. Hence, it is necessary to form bolt threads to special limits to accommodate the coating.
- There are two different methods of manufacture which take into account the necessary clearances for the HDG coating applied to fasteners.
- The usual method consists of using nuts tapped oversize to tolerance class 6AZ or 6AX after coating, to mate with bolts manufactured with threads to tolerance position g or h before coating. AS/NZS 1214 provides detailed information on tolerances for bolt manufacturers and marking requirements.
The galvanized coating on the thread of the stud or bolt will provide corrosion protection for the internal thread of the nut.
Figure 35 – Internal Threads