So all you’ll need is the following:
1 card board box tab
1 Set of numbers (not sold in sets, sold indivdually. )
1 box cutter blade
1 magnet strip
So it pretty simple just adhere the sticker numbers which are a then sheet of metal that has adhesive on the back. And cut the cardboard following the shape of the numbers. Then place a magnetic strip onto the back secure with hot glue or gorilla glue let it set and place onto your door.