Man, I used one of the ND filters that came in the FMC and it was super tight. I could not get it to completely rotate to the on position.  Then when it came time to remove it was a @#$%&%$ b*&%ch to get it off.  These things are a POS.  I don't think I'll be using these anymore.  Hopefully the variable ND's I have coming from Moment will be more user friendly.