Wheel adapter studs?

Sorry for the confusion, I typed spacer when I meant adaptor.

Both are perfectly safe as long as you use a quality part and do your proper maintenance. Obviously there are size limitations for both, spacers can only be so thick before you need to upgrade the strength of the studs and obviously you need enough stud length for proper thread engagement. Adaptors can be much thicker, but eventually the material makes a difference.

Dually trucks all use adaptors. Thick about the loads and torque carried by some of those adaptors! It's just about having an adaptor that's been built to carry the loads that it will see in operation. And checking both sets of lug nuts for proper torque.

For example, the adaptor used on an F350 dually 4x4. It's almost 5" tall, and no, there aren't any splines or anything inside of it to attach it to the axle. The strength is simply a factor of the material used for the adaptor and the size/number studs.

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Those are different. The cheap ones you get to adapt one wheel to a different wheel pattern on your vehicle are the ones I'm talking about. A friend of mine lost a wheel cause a few studs broke. cheaply made.