One has to determine the thread size of the lathe spindle so that you can get a chuck that fits your spindle. There are a variety of lathes in the market which have many different sizes of thread on their head stock spindles.
Look in the manual or any pamphlets that comes with your lathe. The thread size should be listed in either one of these materials. It should be in the area where the machine make and model are.
If for some reason you do not have any pamphlets or manuals, contact the manufacturer of your lathe mill.
You can also look up and refer to a Teknatool Lathe listing. If you find a match, then this will be the chuck you need for your spindle. If you do not find a match, you will need to measure your headstock spindle diameter accurately. You will need to figure out if it is a metric thread or imperial thread.
If you are unable to determine the size of the lathe thread with the above steps, take your faceplate to your local teknatool store. They can contact the manufacturer or engineering company.