the corner piece of a chep pallet. about 4x4 and kinda hard. (i work in a warehouse and we dont really have tools so we have to improvise.) or what I have done is clamp it in a good vice-grip and use a railroad tie step at my folks place. for straightening nails honestly wood is better than metal. if you the need the strength of metal I would ask around at machining shops or welder buddies, an I beam or solid c channel should do ya. prolly free if you are friends. also you can use your hitch in an pinch.