Showing skid plates for: transfer case and fuel tank
uses 5 M8 bolts on front side -- with existing threaded holes
uses a plain hole on the rear side -- M12 nutsert fits great into that hole
After being sanded
M12 nutsert in place
Nicest option is inserting a nutsert into the existing plain round hole -- this requires a nutsert (M12 is the correct size to fit the hole) and a rivnut tool ($40 on Amazon, comes with M12 tip)
The alternative is just using a nut and bolt of your choice
form a threaded nut connection inside of a stock plain hole
shown is an installed nutsert for transfer case, next to installed Fuel tank skid plate
Nutsert closeup
Nutsert (left) is used with a rivnut tool (and right sized tip) to form a nut inside of a round hole
Nutsert collapses in the grooved area (right) when installed, holding a bolt in place