I received another bunch of emails from people worried that their ER Spindle nut was incorrectly manufactured. So I figured I'd mention it here.
You can see that there's an eccentric ring inside the nut. This is what throws people off. They insert a collet into the spindle, try and screw the nut on and it won't go on, or throws the collet off axis. Then they look at the nut and assume that the nut is defective as the ring isn't concentric. It does look wrong.
The proper way is to insert the collet into the nut until the eccentric ring snaps into the groove in the collet. This allows the nut to pull the collet out of the spindle when loosening it.
Then the nut is screwed on loosely, then the tooling is inserted into the collet and tightened fully.
Taig started putting a sheet explaining this in with the mills, but not the new 1045ER adapter, and who reads the paperwork anyway?