kant section 13 how is pure math possible

"What can be more similar in every resoect and in every part more alike to my hand and to my ear than their images in a mirror? And yet I cannot put such a hand as is seen in the mirror in the place of its original, for if this is a right hand, that in the mirror is a left one, and the image or reflection of the right ear is a left one, which never can serve as a substitute for the other. There are in this case no internal differences which our understanding could determine by thinking alone. yet the differences are internal as the senese teach, for, notwithstanding their complete equality and similarity the left hand cannot be enclosed in the same bounds as the right one'

I think Kant is saying how there are internal difference between things that can be the same. These things may seem to be equal but they are not because of their internal differences.