On my wife's Suzuki their M10 will not work with a 3/8" socket, and if you get into anywhere serious on a GM or Ford - those bolt heads will be exact metric with no room for imperial.
The ford I had had a surprising amount of imperial on it about a decade ago. Presumably under the hood and inside the engine it was all metric though.
I can verify its 30 mm with my wheels/hubs on my car. Supposedly that's "unusual" and most cars that size are 28mm or 32mm so people end up mystified why their 28 doesn't fit something that looks visually at a distance like a 28, or they use a way too big 32 and neatly round off the corners of the nut when it slips. I imagine using an imperial impact wrench is an effective way to round off the wheel nuts on a Saturn.
I would imagine if you bought aftermarket wheels/studs alloy or steel you could have most any size within a narrow range that's compatible with the hub.
"hitch"
LOL at the idea of my tiny little 2-door subcompact towing anything like those giant RV trailers. I do know standard american trailer hitch on pickup trucks has been 2 inch square for a century or something like that. Kind of like how we're not going to change every piece of railroad track and rolling stock in the USA to a metric equivalent rail gauge any time soon, until the end of time we'll be stuck with 50.8mm trailer hitches. I bet you could slam a european 50mm in the hole within manufacturing/rust tolerances.
The explorer is metric in a lot of places. The engine is SAE since it's based on the 302 which was originally designed in the early '60s. Pretty much anything that was designed from the mid 80s or later will be 100% metric hardware unless it needs to work with something that isn't. And even then it'll will sometimes be metric until it hits the non-metric piece. For example, the Tremec T-5 transmission is metric but mates up to the Ford 302 which is SAE.
So basically, it's usually metric except when it's not.