These cool little plastic lenses are 3/4" diameter x 1/4" deep, have two little knobs (which I'm sure could be cut off with a sharp blade), are concave on one side & has a slight set back on the other so you could put something underneath it. The further away from an object that you move it the more fisheye the effect. Notice the text in the photo above. They are plastic so might have small scuffs or scratches.
2 per pkg.