Because people have a need to glue things to other things
Metal to GlassFor the strongest, fastest, and most invisible bond we recommend:
Maybe you are gluing a rear view mirror.
Whenever you are gluing glass you must consider the visibility of the adhesive. If the glass is translucent or transparent, you will want a glue that dries as clear as possible.
Whenever you are gluing metal it's a good idea to clean it first with steel wool or sandpaper. (Rust never sleeps.)
Before gluing any glass bond be sure that the glass is clean, free of any oil (even from your fingers) and dry.