This is a mask set for the Airfix Grumman F4F-4 kit recently issued by Hornby-Airfix. It consists of a small sheet of yellow masking paper die cut so that the parts required can be easily removed without damage and applied to the areas to be masked. These include the clear glass areas of the cockpit canopy and the armpit windows below the wing. They fit exactly, and should quicken the painting process.
These are worth getting, and would be useful on the Hasegawa and Hobby Boss kits as well.