Rivets for mounting the valence to the Grill

http://rivetsonline.com/rivets-en/semi-tubular-rivets.html

I used these in various sizes all over the car.

Ashtray
Grilles
Wiper Motor
Switches
Heater Box

To name a few!
Thank you!
This looks promising. I can measure the thickness to get the length of the rivet and the matrix gives a suggested clinch allowance.