There are two different types.
For original drums, use the "glue-on" type that attaches to the drum and supports the wheel on the inside of the bolt circle, but does not space the wheel outward, so no stud threads are lost.
For new repro drums, use the type that fits over the studs - this serves two purposes; supports the wheel as the first type does AND spaces the wheel outward to clear the edge of the drum center. The new reproduction drums usually use longer studs, so there are still adequate threads for proper lug nut installation. These SHOULD NOT be used on original drums, as threads will be lost, causing the studs to be too short for proper lug nut installation... 3 threads exposed when the nuts are tight.
We stock both types... failure to use them results in not being able to properly
tighten the lug nuts due to no support inside the bolt circle, with the result that
the nuts will come loose and allow the wheel to "work" and elongate the lug holes
-OR- the nuts have the crap tightened out of them in an attempt to properly torque them, with the result that the wheels crack around the lug holes, and
eventually come loose and further ruin the wheel.
Note that the "inside-mounted" drums (so-called 46-48) may have weights that
interfere with proper installation/seating of the wheel on the drum. In the "old
days" spacers were available to move the wheel outward to clear the weights
BUT this also results in loss of threads available for the lug nuts as per above.
Therefore, the least-worst choice is to grind the weights away and then have
the wheel balanced ON THE VEHICLE, which will take care of any imbalance in
the hub/drum. IF this is done, it is important to mark the orientation of the wheel
vs. the drum so if the wheel is removed, it can be re-installed in the same position...