My original studs were one size (7/16 I believe) and the spacers were one size larger (1/2). I had typical chrome lug nuts originally. I had to get open acorn nuts for the original nuts inside the spacers (will make sense when you get yours). Only "problem" I really had was that my 4-way wouldn't fit the new studs and clear my rims. I had to get a thin-walled socket for that. But, if you figure out what size yours are now and notify them of that size when ordering your spacers, they will put the same size studs in them. On mine, they said they would sip me some new studs to replace myself or I could ship the spacers back and they would do it. I decided to live with the thin-walled socket approach.
One other thing, many places won't work on tires/wheels mounted using spacers. Discount Tire woudln't work on my wheels because they were mounted with spacers. Their policy is that they could only mount a wheel as long as it made full contact with the drum. They could remove them and work on my tires, but when re-mounting them, they would have to do it without the spacers. I talked the manager into doing it anyway, but that is the ONLY issue I have run into so far in regard to using spacers.