Yes there is stuff inside: antenna, sunroof drain, and wires to the dome light.

 

First your drill a hole the same size as your rivit and you get a rivit gun (they are pretty cheap) and you put them in it and squeez it and as it squeezs the part that you stuck in the whole expands untill there is too much presure and it pops...

it ends up looking somthing like this


but in silver or black...which ever color you buy....

ill take pictures of my guage pod when i get home so you can see.

 

just use cable ties. looks ghetto but hell if your car is fast who cares what it looks like

 

My buddies integra used the Autometer push plastic plug connector things:

But with the pillar weight he also had a single screw going thru a plastic washer to make a level surface for the screw head going all the way into the A pillar metal itself...