The 5 lower holes are used with screws that already exist on the lower edge of the bumper. You would need 3 self tapping screws for the top, just need a coarse thread to screw into the bumper and hole it in place, I recommend stainless hardware or zinc so it doesn't rust, and using a rubber washer under the screws up top.

There is no standard size just go to Home Depot and get 3 screws that are long enough to screw the top portion in the bumper, and are small enough to not be too thick to fit in the holes on the skid plate.

Make sense?

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2018 Ram 2500 6.7L Cummins 68RFE
19k miles -Bright White/Black - Big Horn Sport - Crew Cab Short Bed
2013 X5 35D (CEO's) - Born on 5/17/2013 -
82k miles - Alpine White/Cinnamon Brown/Premium Pkg, Sport Activity/Premium Pkg and Sound/20" Style 214/Running Boards