I had the same question when I bought mine! It is quite possibly the most wonked up way to keep an access panel shut there ever was. You have to take the bolt assembly apart, thread it through the hole on the bottom left side of the lathe, put the spring on the bolt and blindly screw the nut to the bolt. Then, it works by pulling the bolt out with the knurled knob and pushing it to the side while opening the door. Seems they have never heard of a simple twist knob.