This is my first robotics experience, outside of one class 10 years ago. I've been Googling this question for about an hour but I can't find an answer!
I'm using a ROHS Step Motor 28BYJ-48 (with an Arduino Uno). The rotating shaft that sticks out of the step motor seems to be called a "double-flat drive". It's less than 1/4" wide, and is flattened on two sides.
I need to attach a 6" long arm to it, so the arm can spin like the second hand on a wall clock, but in both directions. What can I use to attach the arm securely to the shaft? What's the name of the part that will couple this double-flat drive shaft to a straight, flat piece at a right angle to it? Or are there flat metal circles with holes in them that can be coupled to the double-flat drive shaft without slipping - and what's the Google search phrase I should use to find them?