My apologies for not explaining, as Silyavski mentioned that is the MGD16 and the other one is this http://www.automation4less.com/store....asp?prod=HD16 and if you notice there is a .4mm difference in diameter causing the issue since the ballscrew I got for my Z and Y are from taiwan and support MGD size only, I find it kind of big for Z but I think I will do the design adjustment anyway.