Yes, you need the stud extenders to mount the center plate and weights; 8 per side times two wheels equals 16 total required. Nobody repops the extenders anymore, I think STEINERS did at one time but no longer do. A few fellas have made their own. TOH (The Old Hokie) made some sets to sell a few years ago but don't know if he has any left nor if he still makes them so try him. You don't 'drive' anything out, they screw onto the existing wheel studs and allow the center plate to mount to, thus extending the male thread end to accept the lug nut. I have a complete set of the HD (45#) weights and a few sets of the stud extenders but won't part with anything, so don't ask. I'll try to take new pictures and post later, PhotoPhucket won't let me post pictures anymore. The stud extender has a long 1-1/16" hex with a 5/8-18 2B female ID that screws on to the existing wheel stud. The plate mounts on those, then the extended 5/8-18 2A male end accepts the lug nuts.
Tim *PloughNman* Daley(MI)