This pair of 1"x2" size .002" thick brass sheets are ideal for flossing between the nib tines on your fountain pen to keep your ink flowing smoothly. Use it periodically when you're cleaning your pen to clear out crusted up ink or lodged paper fibers from your nib.
The brass sheets should be enough to last you quite some time if you're careful. The brass is soft and can be bent fairly easily, but when that happens you can use a pair of household scissors and cut a small sliver off the end to reveal a fresh new edge to your brass. The reason the brass is so thin is so that it will easily fit between your tines without causing any pressure that would misalign the tines. Brass is the ideal material used for flossing nibs because it's softer than any other metal used for making fountain pen nibs, so it won't cause your nibs functional harm. There is a potential for the brass to scratch a nib with a colored coating on it (such as the LAMY or Monteverde Black nibs), so be careful when you're using it on nibs like these that you don't touch the brass to the nib surface.
To use a brass sheet on a nib that's installed on a pen, insert the corner of the brass into the slit of the nib on the opposite end of the tip. For most nibs, there will be a hole in the middle of the nib face where you'll insert it, but some nibs don't have a hole (like Lamy, for example). Slowly and gently drag the brass sheet towards the tip of the nib, making sure to keep the brass between the tines as you go. Be careful not to jam the brass too far down into the nib, as you will hit the feed if you do that. Try to keep the brass pretty shallow in the nib. Once you've reached the tip, the brass will be tighter in the nib as nibs are designed to touch at the tip. Once you've pulled the brass all the way down through the slit, you are all set. You're welcome to repeat it as many times as you feel necessary. You can do this with an inked or uninked pen, but in general it's best to floss your nib during your pen cleaning process, and flush it out after flossing.
To use brass sheet in a nib that isn't installed in a pen, do the exact same method as above, but on the underside of the nib instead of on top. Flossing with brass sheet is also a good practice if you're doing any kind of nib smoothing, to remove any small metal particles from the nib.