Internal threads and nuts must be tapped oversize after galvanizing to accommodate the thickness of the galvanized coating on the stud or bolt. The galvanized coating on the stud provides corrosion protection for the internal thread.
For economy, nuts are sometimes galvanized as blanks and threads are tapped after galvanizing. Uncoated internal threads are acceptable since the zinc coating on the external thread provides full corrosion protection.
Bolted assemblies should be presented for galvanizing in the disassembled condition. Nuts and bolts or studs for galvanizing should also be supplied disassembled. When internal pre-tapped threads included in components are required not to be galvanized they may be plugged temporarily by means of bolts or studs screwed fully in.