It depends on which end you plan on using the collet for.
If you are using it on the tip end,you MIGHT be able to get the small end down to .562/14mm,with a slightly bigger lip to stick out of the front of the chuck,but you'll be happier with a .625 shank and a 3/4 lip on the OD,then whatever size you need on the inside.
If you are using these for the joint end,then the inside bearing diameter will determine how big that end needs to be,plus 1/8 for the lip.
On the joint end,you'll need to cut the inside on about a .010-.015 PER INCH taper on the inside,which isn't much,but trust me you'll NEED it. Tommy D.