It is a set of 3 rubber for your Game Boy Advance console : A,B buttons - Directionnal pad - Select,Start buttons.
Your buttons are tired or didn't function anymore ? Maybe the rubber of the buttons are spoiled. This set of new rubber can revive your console.
To open the console, you'll need a
triwing screwdriver that you can find in my shop.
I have a lot game/accessories for retro and recent consoles on my shop !