I'm doing this thread for the folks that haven't been initiated to a shrinking disc yet. There is still a lot of doubt as to their usage and effectiveness.
I'll start with the discs themselves and mounting them. You can use any grinder that is big enough to handle the job, as long as its rated for the size of the disc. You will probably need to buy a thin mounting nut. I use a Milwaukee nut, available at most tool stores. The thick nuts that come with your grinder will protrude beyond the surface of the disc, so that you cannot place the whole disc on a flat surface without the mounting stud or nut protruding past that surface. I've tried about everything I could think of, and I have found that old worn out flap disc pads are good for spacing and mounting the discs. And don't ask what the sharpie lines on the small disc are for either. I can't remember.
I'll start with the discs themselves and mounting them. You can use any grinder that is big enough to handle the job, as long as its rated for the size of the disc. You will probably need to buy a thin mounting nut. I use a Milwaukee nut, available at most tool stores. The thick nuts that come with your grinder will protrude beyond the surface of the disc, so that you cannot place the whole disc on a flat surface without the mounting stud or nut protruding past that surface. I've tried about everything I could think of, and I have found that old worn out flap disc pads are good for spacing and mounting the discs. And don't ask what the sharpie lines on the small disc are for either. I can't remember.