Crossword puzzle clue "tool in a glass case"

Tool in a glass case?

Like the glass, when viewed by someone who's pessimistic about how much liquid is in the glass

Small glass disk used as an ornament in a stained-glass window

Vehicle with a glass case

They work on a case-by-case basis

Something done on a case-by-case basis?

Ones working on a case-by-case basis?: Abbr.

___ case-by-case basis