The Taig 200-00ER is a complete ER16 headstock. If you have an older mill that originally came with the ¾-16 headstock this is a bolt-on replacement that will change it over to the newer style ER16 collet system. The ER collets offer a much wider grip range and lower run-out. This headstock comes with the closing nut and you can swap the pulley over from your old headstock.
Also, take a look at our selection of ER16 collets at the bottom of the page.