Definition - What does Threading mean?
Threading is a manufacturing and metal processing method used to create the helical detailed edges of a screw to enable it to be fastened to another piece of wood, metal or material. Threading may be the source of corrosion in some materials due to the crevices created by the process.
Corrosionpedia explains Threading
Due to the crevices created by threading, screws, bolts, nuts and other fastening devices may be more prone to crevice corrosion, which is more likely to go unnoticed due to the depth of the corrosion site. Materials that have been threaded should be examined regularly for signs of corrosion.
Understanding Corrosion in Pumps and How to Deal With It