If the turn signal is in the off (center) position, the plastic nub is retracted and the steel arm fits in there. When you turn on your turn signal, left or right, it pushes that nub out, and then the arm swipes across and releases it. I think. I do know that if you accidentally put the turn signal on, left or right, then put the steering wheel on, you will break it off and have to manually cancel your turn signals from then on.