These thin brass sheets (0.002" or 0.0508 mm thick) are used for working on removing paper fibers or dried ink out of the slit in fountain pen nibs. This package includes 2 1"x2" sheets.
Whenever working on a nib caution should be used for two reasons. First if the pen is under warranty any nib work can void said warranty. Second, damage can be done if the user is not careful with gold nibs and scratches on the inside of the tines can impact ink flow.