The Screw Chuck
A screw chuck is a small faceplate with a short screw coming out of the center. In order to attach the screw chuck, you must first drill a hole in the bowl blank.
After drilling the hole on what will be the top of the bowl (the side withe cavity), simply screw the chuck into the hole and tap the chuck taper into the corresponding taper on the headstock of the lathe.
The Four Jaw Chuck
The four Jaw chuck is a method to hod a workpiece on the headstock by the unfinshed foot. Each of the jaws can be turned seperatly to facilitate the gripping of odd shaped materials.
The Compression Chuck
The compression Chuck is a good way to hold an almost finished bowl by its unfinished foot. (see link for operation and construction.)