You will probably want to put a couple screws in each side. Just transfer measurements from your oem tips. A little trickier to do with slash cuts, as you will need an accurate reference point to get them both the same.
What he said. Just take off your old factory tips a save the screws. You'll need to drill two mounting holes in the 18" Airflows.
Transfer the holes from the old tips to the new ones......measure once, twice and three times.
