It's real easy actually, just slot whatever part of the pad lip into the "cut", so that the lip is like halfway in the groove, halfway out, and turn the pad "away" from the groove, while lightly holding on to the first part where it's already in the groove. Once you complete a whole round the lip will pop into the groove easily! i cant upload photos due to newbie restrictions, but i made a short video on youtube:
http://www.youtube.com/watch?v=CaDRTS4UrXs&feature=youtu.be
I sorta discovered it cus i was turning it the other way round and the lip got "caught" in the "cut" and i was wondering why the lip kept going in where i was pushing in and coming out the other side! duh...


































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