Thats what I'm referring to. Not the little rings that don't have studs.
Here's what I run: They are 6 lug spacers from marlin crawler:
They have their own lug studs which are pressed into the spacer. They do not alter the pattern, just add 1.5" thickness per side. Cost is about $85 a pair, at least from Marlin. But those are 6 on 5.5".. Check spidertrax.
Here they are installed on my Toyota: You can see the 6 holes, thats where the spacers are bolted to the hubs. Then the 6 new lug studs pressed into the spacer. Thats a reason you don't want to overtorque them. I'ver heard of someone having the stud spin in the aluminum when they tried to remove it(also overtorqueing can make the studs snap under a shock load).
In general, follow the rules and they are perfectly safe. I'm leary of going beyond 1.5-2" or so, but in reasonable sizes, I see no problem