Backporch:
There are good spacers and bad spacers; and design has as much (?more?) to do with it than country of origin (poor design and less desirable country of origin due tend to go together though) At one time or another most (all?) of the big 3 have run spacers on their 1 tons so they could use same front hubs for both SRW and DRW trucks.
What to look for:
Is the spacer hub centric; machined to Ranger hub diameter? (Asking spacer bolts to hold wheel concentric and then hub bolts to hold spacer concentric is asking for trouble).
Is the spacer thick enough to extend past existing hubs? (15-25mm spacers are at issue here than the 30mm+ which we are talking here)
Are the nuts provided with the spacers thin enough to be below the surface of the spacer? (Rim sitting on the lug nuts is recipe for disaster).
Are the heads of the bolts 2X diameter of bolt - assuming Aluminium spacers. (Using regular bolts, which are designed for steel, is asking for them to pull through - heads are just too small).
Note: 6061 T-6 Aluminium, which is what most aftermarket spacers are made out of, is ~75% yield strength of cast iron, which is what was used in the 1 ton spacers.
Last: Are you using spacers to put contact patch back where Ford Engineers intended it? e.g. Mustang rims on Ranger. Or are you using spacer to do something you probably shouldn't? e.g. 4" spacer for F-250 so you can run dually rims on back. (Then pretending truck is F-450 and loading a camper.
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p.s. I was lazy and didn't mount the spacers on the back on my Ranger before installing the Mustang rims last time around. If one wasn't told to look for it, one didn't notice the 30mm difference. The front on other hand made bad noises pulling into parking spot at mall, so the spacers were quickly reinstalled.