DnD Spell Area Effect Corner Template Markers

When playing Dungeons & Dragons on a grid battlemap, there is often the need to mark out areas with a magical effect. I have seen templates or frames being used to mark these areas, but none of them felt satisfactory. They are often large and difficult to lay down on the map. Their large sizes often mean they can break easily and are difficult to transport around. In reality, there is no need to mark out the entire effect area with a frame or template. All that is needed is to mark the corners of the affected area. And that is what these corner markers do. They can be stored flat in a container and when they are needed, just fold and lay them on the battlemap to denote the area effect's corners. Boost MeLike this design? Give me a Boost!