I want to say 18mm. A quick breakdown on how t do this:
1) spray the bolts the night before with penetrating oil to loosen them up
2) measure the current fender height for a reference point
3)block the back wheels and jack the front end up until the tires just come off the ground
4) turn each bolt lets say 4 whole turns for starters
5) sit the truck back down and check the new fender heights
6) adjust side to side if needed or add a liitle more to both to get the look you are after
7)don't crank too much, ensure the control arms have some space between them and the bump stops
8) if all is good take a quick trip around the block to cycle the suspension a little and settle it back down. Double check the heights after that.
9) if you are happy with the heights after the drive go get an alignment.