Missed this thread, that's when I was MIA. I recently got me a set of the ER-40 blocks too along with their bearing nuts. Luckily my collet wrench fit them.
I love these things. I have a super spacer but there were so many times where I just needed to quickly cut 2, 4, or 6 sides. Sucked having to lug the super spacer onto the table & indicate only to spend a minute or 2 or milling. The super spacer is heavy.
I was also suprised when they showed up the next day! One day shipping all the way from the UK!