These are 4.5 mm safety eyes with metal backs - the ones I use for all my toys.
The metal back has a 'flat'side and a side that has two little 'wings'on it.
Align your toy pieces so you can create the eye holes at the same time.
Use a metal meat skewer or a large doll needle to make the hole.
Using some felt scraps, cutting out two rough circles. These need to be just a bit larger than the metal back. These are our felt 'washers'. Skewer some holes in these as well.
The 'washer'stops the ridge of the metal back showing up on the front of the toy after if it is stuffed and provides a buffer between the metal and the fabric/felt.
Lay your toy pieces out so you can be sure you will be making a right and left side of the toy.
(Trust me this is important)
Place a 'washer'over the eye post on the inside (wrong side) of the toy.
Place the metal back in place on the eye post with the flat side against the felt. Using both hands press the metal back into position. You will here a little noise as the prongs on the wings grab hold of the eye post.
(I know , I know but I needed the other hand for the camera)
Press the back as far onto the eye post as possible.
Easy as winking !