How can you make brass knuckles fit better and reduce damage to hand?

Answer 1

Much the same way you would make a traditional ring fit better--if it's too big, cut a portion out of the fingerholes and solder them back together. Too small? insert a piece instead of removing it. You can also file the edges to round them out, so they don't dig into your fingers. However, if the impact is what's hurting your hand you pretty much have two options--increase the surface area that touches your hand (this will spread the force of the impact more evenly and over a larger area, thus reducing the force against any given point on your hand--basic physics) or wear padding (gloves). Good luck, and please don't kill anyone. ;)

Answer 2

Kind of a disturbing question, but I'd guess you have to get them made to fit your hand. It's just a solid chunk or metal, not much you can do with it. You could try wearing gloves with them, to protect your hand, but that's about it.