Hey Wayne, hey Andy, hey all,
I think you mean collets, not nuts.
This is asked frequently here: ER collet
A collet has to match the bit shank diameter so you need one for each bit shank diameter that you use. With ER-20 collets, you can use tool shanks from 1 to 13 mm (including 1/2" – if you get one for 1/2"). For mounting the collet inside the nut correctly, see here.
Usually they sell ER collets in runout classes. 24,000 rpm spindles are high frequency spindles, I would buy collets with 5 µm or less runout (class 1). The less the collet runout, the longer your spindle bearings will live. It also depends on tool however, and of course of the runout of the spindle itself.
I bought my 5 µm set of collets here (a unboxing video).
15 µm runout (class 2) collets are cheaper, e.g. here.
Further video watching
ER Collet Essentials. Do You Know? – Haas Automation Tip of the Day