skid = (of a vehicle) slide, typically
sideways or
obliquely
They are not intended to protect against every type of slamming down on something
bash = strike hard and
violently
so you want bash plates if you intend to really fall/crunch on something. those you probably have to make yourself
factory skid plates, on '97 they came stock, not even mention of them in the brochures, later, they were either options or you had to get an FX model.
They are on the xfr case and the fuel tank. some apparently came with a third skid in front but I never seen one (if you have one, post it?)
they are intended for situations where you have misjudged clearance a bit and you are "skidding", or sliding, over something sticking up and they help to keep that object from catching on the xfr case or puncturing the fuel tank. if you think you are going to be in a situation where you will fall down violently onto, say, the gas tank, then you need something else. skids will protect against skidding across something but not against almost 2 tons of metal pushing down on one spot in a fall, for that you need something that can support all that weight.
and of course when you add thickness you are reducing clearance but that is perhaps a non issue.
Don't forget your diff's are much lower than anything so is it possible you clear them but don't clear stuff higher up, it's possible, but all that other stuff is substantially higher. I'm not saying it can't happen, of course you can have situations where you clear something then the front wheels go into a depression, I imagine anything -can- happen. Along those lines I'd like to hear if anyone actually had catastrophic damage in places where plates (skid or bash) would have helped. And I don't mean rock crawlers, just a well set-up trail rig type of truck.
So you might want to look at guards for the diff's, they make them, again putting them makes them lower so you are more likely to have the thing happen you didn't want (diff catches on something).
Just like auto hubs, Ford doesn't claim these are the be-all for offroad. They can help in some situations where you will mess up the skid plates and not something else. Again, for sliding over something where you didn't quite clear it, not for a hard fall onto something. I think, unless you find something 3rd party, you would want to find a good experienced metalworker/welder and have them construct something out of 1/4" steel or something like that. To me, a lot of it is avoiding it happening, so maybe larger tires, lift as necessary, and be careful to note potential danger situations. Other guys will know a lot more about the potential risks/solutions.
And of course even if you go to larger tires, from 31" to 33" you are only adding 1" of clearance to the diffs. The lift would help on getting the other stuff up a little more. Nothing will protect against every possible situation. Obviously the ideal is you have a completely smooth and protected underside but I don't think these trucks lend themselves well to doing that.
I'm interested, because I'd like to know more about front bash plates/guards but then you look at the front of the truck, rad and other stuff is up way high compared to bumpers let alone the front diff and the beam that goes across there so I don't get exactly how that would work. And I'm not against having something made that's ruggeder, if it's warranted.
Pics of the 2 oem skids on mine below.