Croco Models from Latvia specializes in aftermarket detail sets and resin sets, mainly of armored vehicles. They sure know how to find unique and interesting subjects. Visit their webpage and you will see.
Besides aftermarket details and resin kits, they release small generic detail parts, in this case a perforated metal plate, with very small circular plates in a diamond pattern.
The size of the fret is about 2 inches by 1.25 inches and it can be used for detailing many different models, probably armor in 1/35 scale (engine covers), perhaps aircraft in 1/32 and 1/48 (air intakes filters).
You can see how finely and homogenous the perforations are, as you can “see-through” them and still see the mini-ziploc bag behind it. Just think of it as a way to dress up any opening towards the interior of a model where you want to make it look like there is “something there”, like a radiator, a screen or just “something” which is better than bare plastic.