I am going to assume, that your bars are the right hight for you, and your getting Brass Knuckles so you have to cut the slit off, ( Which is about two inches ) so you can put the Knuckles on and still have your height. Tell me if i was right

Anyway just use any old handsaw, you could use a circular saw but i usually just clamp them down and do it old fashioned with a handsaw.