The kids and I found brass knuckles on thingiverse and thought rubber knucles would be really funny. So here they are. I use Oogoo for casting these brass knuckles and you can find the recipient here: http://www.instructables.com/id/How-To-Make-Your-Own-Sugru-Substitute/ Oogoo sets in less than 10 minutes so printing molds is a great way to build an army fast :). Add a few drops of essential oil to the mix and after a few days your object will smell like that instead of vinegar. Have fun.