Following on from the discussion about magnet types on the 515E in this topic http://www.hostboard.com/forums/f700...rice-515e.html

I've noticed that the 515-xG followed the 515E with the rounded back style magnet.
I have seen though, units with just a rounded back, and units with a rounded back and bolts holding the magnet on?

Any thoughts on the differences, if any, and why the design alteration.