Mounted below the surface of

SET INTO

Think of how a gem might be placed in a ring or a tile in a wall, ensuring it stays flush and secure. This phrase describes embedding something firmly within another material.

The clue "Mounted below the surface of" hints at something embedded or fixed within another material. "Set into" fits because it describes an object placed just beneath or flush with a surface, like a gem in a ring or a window in a wall. The phrase plays on the literal meaning of installation or insertion, making it a straightforward definition without hidden wordplay. Think of how a tile might be set into a floor—it’s secured but not protruding.