I got a package of 10 grates for $1.59. They only come in one color and size (at least at this store), but you can make triangular and hexagonal shapes.
Me, I was looking for the ubiquitous AK-47 look.
A little blurry, but you get the idea. The rifle stock was flattened with needle-nosed pliers, as was the magazine, then clipped with sharp scissors or a craft knife to make the shape a bit better. On 15mm figures, it works.
One of the other issues I have been having is creating crests on hoplite helmets. Using dimensional paint works, but it takes layers to get a good result, which takes time and patience. This new triangular shape fits nicely around the curve of a round-head furniture plug.
Add just a little dimensional paint (one layer, in this case) and it makes a fine horsehair crest for a 15mm helmeted head.
Not only are there triangular grates, there are circular ones, with curved rows and columns. I could not think immediately of a use, so I did not buy one, but I am sure I will come up with something later, like gears.