Each disc has a whole in the middle of it. Attach each disc to whatever surface you are working with with a screw or equivalent. Then you need to gently hammer or force the two discs together. They are locking discs and once they are locked they are extremely difficult to pull apart.
These are much better than typical Velcro because they will not loosen over time.
.815 dia with .16 hole. Buy 2 pcs to make one snap, 8 pcs to do all 4 corners of a speaker grill. Can be screwed, glued, and/or stapled on.