What you need is a lathe chuck to fit the 1X8 thread on your lathe spindle. A chuck can work but there are better (maybe) and less expensive ways to support your pot blank for turning. You need to study the tutorials section on making pot calls and watch some video's. One easy way to support the pot blank is to drill and tap a center hole (I use 3/8x16 ) and convert the faceplate that came with your lathe to a screw chuck.
To convert the faceplate just screw the faceplate to a block of wood and then turn the block round, drill and tap (to match your blank) a center hole through the block. Now face the block so that the outside surface is perpendicular to the hole. From the back side, screw a bolt through the block so that about an inch sticks through. Now you have a stud that your blank will screw onto. Now turn your blank round. You can also use an expanding mandrel to accomplish the same thing but you will need a collet chuck to hold the mandrel.
Here is one video to get you started:
