I used to work for the Federal Bureau of Prisons. You would not believe what makes a great knife, and just how easy it can be made, then made to decompose, and be flushed away. Funny, one weapon used in the style of Kung Fu I studied was quite simple, and there is nothing illegal about carrying it. You usually make the wooden handle slightly smaller than the width of your palm, and the blunt steel part. 1.4" (.250") in diameter, an inch long. You'd be surprised how a series of quarter in diameter, one inch deep holes in your head will ruin your day. Actually, any place on your body, this will disable you. If you know pressure points, the injuries are permanent.