ER collets on a Super 7 Myford Lathe

Depending on your work, there are collets from an ER8 with a small size of 0.02 inches up to an ER50 with a large size of 1.33 inches. I've checked the Myford website, and they no longer seem to have ER 25 chucks available for the small bore, but they do have them for the ER 40 and the ER 32 size collets. Different kinds of nuts can be used for various types of applications. Consult the manufacturer's specifications for the type of nut most appropriate for your applications. There are more ER chucks than imaginable for the ER series collets. Pick the one that's most appropriate for the size you want and for the size of your particular machine. There are many websites on YouTube explaining ER collets with a lot more detail. Sites like Joe Pie, Abom79, or Blondyhacks, are to name a few.
I did not mention it in the video, but the cleanliness of the spindle and the interior of the collet is extremely important. They should be cleaned with a clean rag every time you take them apart and put them together.