I'm not sure if you've checked out other threads on this topic, but you should know that 3 1/2 exposed threads is NOT enough to adequately and safely support your rear wheels. There are many horror stories from people who have lost wheels while driving due to the use of wheel spacers like the ones you bought. If your wheels haven't fallen off yet, consider yourself lucky.
Spacers are OK if you use the right kind. H & R is a reputable company that manufactures hub-centric spacers. Their spacers have another set of studs that come out of the spacers themselves. They also have an extension of the hub, which looks like a little lip around the center hole in the spacer. This is what the wheel is actually designed to sit on, rather than on the studs. There is too much stress placed on the studs themselves when a spacer like yours is used.
Be careful! Maximum Motorsports sells H & R wheel spacers; check out the pictures and you will see what I'm talking about.