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Not sure about wobble rollers but have seen them on the outside of standard roller U brackets, in fact I have one on each side of the winch post roller.
On keel rollers you use extended pins and stick one either side of the normal roller bracket. They work by stopping gouges in the hull at the keel if you are doing beach launches / retrieve in swell as the hull hits the roller not the bracket. Thse bevelled ones will also help align the boat. Can save somescrapes on drive on setups