These barrel nuts or clips are exactly like the original ones inserted into the trunk for attaching 1967-68 "Mercury" script, and 1971-72 Mercury Cougar "Mercury" Hood scripts. The manufacturer indicates that these tubular nuts fit 1/8" holes. Pin size on those emblems are 3/32".
These clips are also used to attach the 1967 quarter panel emblems.
The install is basically the same as shown here: https://youtu.be/mcd788WUNns