TITLE: Example of non-Abelian group with 4, 5, or 6 elements of order 2
QUESTION [5 upvotes]: Is there any example for non-Abelian group in which has more than $3$ elements of order $ 2$, but has less than 7 elements of order $2$?

REPLY [4 votes]: The dihedral group of order $8$ - the symmetries of a square is one such.
It has the identity element and two elements of order $4$ (clockwise and counterclockwise quarter turns). The other five elements are four reflections about axes of symmetry and a half turn - all of order 2.