the ones that actually bolt on are the ones you want, not the type that are a ring and simply slide on.
Also, make sure you buy from a reputable company such as Spidertrax or All-Pro
and NOT the Ebay
cast ones. When it comes to something like these, you don't want to cheap out in this despartment and take your chances.
I have a little over 10K now on my Spidertrax spacers and love them. Haven't had one problem with them or anything of the sort. Make sure they are installed correctly with Loctite on the threads, re-torque after a 100 miles and from there on periodically check the tightness.
The only downfall for me is that the tires sling everything onto the truck. After a drive in the rain, it immediately gets it dirty to the point where it's like I driven a week already in it. It's definitely a trade off, but something I've learned to accept and live with.