Ammonium bifluoride is used as a component in metal and stone polishing products.
Ammonium bifluoride is poisonous so you must be careful when dealing with it.
It is a chemical compound which has a formula NH4HF2 and can be written as NH4F.HF. It is a compound of Hydrogen Fluoride and ammonia used with diluted solutions to scrape glass. It is also used to scrape rust from iron as iron oxide transforms into colorless iron fluoride.