Extracting the spring

Small springs suitable for jobs like this can be found inside spent mechanical pencils or ball point pens. Some mechanical pencils may need to be broken to get to the spring inside.

Once a spring is acquired it will need to be measured carefully. Measure the outside and inside diameter of the spring, as well as its length when fully extended and fully compressed. Most springs of these kinds will have similar measurements to the one in the illustration. If the spring used is different, then the dimensions in the project will have to be adjusted.