Front license plate mount

Search hasn't turned up anything useful on this.

What kind of fasteners are recommended for attaching the front license plate to the plastic adapter that mounts to the front valance?

It looks like M6 or self-tapping screw could be made to work. The adapter has what feels like 3/4" of plastic tube extending back from the hole. I don't want to start with the M6 and ruin half the tube before realizing I should have used self-tapping.

 

These are the screws that came with my front carrier.

 

OK, self-tapping it is.

 

I got Weather Tech license plate frames in Grey as a decent match for Lunar Rock. They included I think at least 3 different sets of mounting screws. These frames have clear plastic over the plate, illegal in CA and many other states. However, I have been using them or similar for about 30 years and only got a fixit ticket once, as a bonus with a minor speeding ticket.

 

Whats so special about Weather Tech license plate holder? I have their mats but can't see plate frame