I have an OTC set of ring compressors. They look like a split piece of pipe. Then there are hooks spot welded to the out side of them. You have a pair of pliers that pulls on the hooks to compress the rings. I love them and hate the band type.
I have the base set. That goes up to about 4 1/2 inches. Then I bought the extra bands for the larger pistons. I have also made a few bands too. Just take some thinner flat steel and roll it. weld on some nuts for hooks and they will work with the pliers from the OTC set.