Hi Chris. They are held with what's called a pin chuck. It's a shaft of steel with a flat ground in it. Riding on the flat is a cylinder, like a dowel pin or piece of a nail which acts as a roller. The pin chuck is inserted into a close fitting tube, and the roller rolls on the flat and jams against the inside of the tube. When the tube is held like this and mounted on a lathe, the wood can be turned without a tailstock.