Cliffy Black Line Protectors
These protectors are precision cut from .010" stainless spring steel. These protectors are CAD designed, and require an accurate playfield scan to get the right fit. They are less than half of the thickness of a standard protector, and are designed to protect the hole edge of a new playfield, or a restored hole. The wood is fully protected under the metal, and the thin edge barely interferes with ball motion. The protector goes to the black line - hence the name.
Here's a Black Line protector on a Monster Bash: