[GCncsuHD]

First, you need to figure out how wide you want to space them out. As a rule of thumb I don't like to use any wider than 3/8" or so of a slip on spacer (make sure you use machined billet aluminum or steel in this case DO NOT use the cheap cast aluminum spacers available all over). You will want to measure your studs, wheels, and the spacer thickness to ensure you will have enough thread engagement, you want to have a few threads sticking through the lug nut if open ended, or at least enough threads to equal the diameter of the stud engaged in a closed lug nut.

From there it jumps up to about 1" minimum thickness for bolt on spacers, although I prefer to go no thinner than 1.25", but likely you will have to cut your studs for spacers this thin as the studs themselves are longer than the spacer thickness. Measure your studs to be sure how thin you can go, and if you are willing to cut the ends of the studs off or not.

As far as the "effect on strength and durability" I could write a book on all the pros, cons, and misconceptions of them.

If you buy quality spacers and torque them down properly you will never have issues. GM, Ford, and Dodge (and other manufacturers) use them in both slip on and bolt on form from the OEM. Think of it this way, the inner rear dually wheel, floating drums, and floating slip on brake rotors are no different than a slip on wheel spacer between the wheel and the hub. Bolt on brake rotors and bolt on OEM dually front hub adapters are nothing more than bolt on wheel spacers.

Do they increase the leverage or stress on the wheel studs? No, your wheel studs do not support any weight of the vehicle. If they do then your wheel is not properly torqued down. Every ounce of the weight of the vehicle is supported by the friction created by the clamping force holding the wheel flange to the hub flange. The only force on the studs should be tension from torquing the lug nut.

Do they increase the leverage and therefore the hub bearings? Yes, of course, that is the nature of the beast of moving the applied force further away. BUT it is absolutely no different than adding wider, more offset wheels. Think of it this way, consider a stock 6" wide wheel with 4.5" of backspacing. Now swap to another 6" wide wheel with 3" of backspacing. The end result is identical to using a stock wheel with a 1.5" spacer which results in the exact same overall backspacing, and therefore leverage on the bearings. Now then if you added a wider wheel at the same time as decreasing the backspacing (for a wide, offroad look) you are actually making a worse scenario than the wheel spacer.

I have ran them for years on several different trucks, 6 and 8 lug, play toys and heavy haulers. I have never had one issue. If you have any specific questions about them I'd be happy to answer them. I could have gone into much greater detail above, but I felt it was already long enough as is.