If you mean rare earth magnets, I've used them. I can't tell you what size to get because it depends on several factors. What are you magnetizing (you said Dread, but weapons, arms, waist, etc)? Will it be twisting or physically blocked and therefore no need for extra magnet strength to prevent it? How heavy and how far is the weight from the pivot point (metal or plastic, etc)? Will you use 2 magnets (one on each side/piece) or 1 magnet and 1 metal pin/plate on the other side OR 2 sets of 2 magnets to prevent twisting?
In general, you're only limited by the size of the model pieces involved. If you let us know more specifics on what you're magnetizing there should be lots of people who can let you know what they used and how well it worked.