Locating pins for the back

I added locating pins for the back this morning. They should be about 15 mm from the edge. So I measured the distance from the edge of the button to the ribs and added 10 mm accounting for the width of the edge. I drilled the whole with the nail I am also going to use as the pin. The diameter is just under 2 mm. The pins were added to both ends of the back. Now I can remove the back from ribs and easily put it back on its place.