securing taillights bezels

Sheet metal nuts, like the side markers should do. Just be sure that you use the size that barely will not slide over the entire stud. If they are too tight, they can break the pot metal studs off.

I'd also suggest cutting the threads first, with them off the car with a nut driver (ratchets and wrenches emit too much torque, if you need a handle, they aren't big enough) and use some seam sealer on the studs, inside and out, when you put them on, to seal the holes from weather.

Hope this helps.