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Generally,
Static load capcity for 16x5 ball screw is around 1240kgf,dynamic load capacity is around 765kgf
For 25x5 ball screw,
The static laod capacity is around 2300kgf ad for dynamic load...

Not sure whether you are means the thread length,
For 2005/2010 ball screw which with end machining for BK15/BF15,the standard end machining length for both is 78mm,that means if the total length is...

1)Use 25mm rail is fine.
2)Seems the length you are need are too longer for internation shipment,as far as know,if ship by express for door to door service,the longest package length are not more...