I made some very simple ones for my kids' kart. I don't remember the exact size- I'll go out to the garage later but I think it was 1/4" or maybe 3/8" rod. I heated and bent the rod with a torch at a 90* angle so it looks like a large L, but upside down. The short side of the L is the pedal, the long side is the arm. At the bottom of the L, I welded a bolt for it to pivot on, and drilled a hole in the frame. I welded a washer partway up the shaft for a return spring to hook on to. Then, depending on whether the pedal is for throttle or brake, the cable/rod attachment is welded on.
About as simple as you can get. Pic later, if I can dig one up.