Thanks for your reply.
I try to use GetChildren for getting RefAxis from cylinder.
But return value is Empty.
The only way to do this is to show temporary axes and then SelectByID2, using the coordinates of where a point will lie on the axis:
Part.Extension.SelectByID2 "", "AXIS", x, y, z, False, 0, Nothing, 0
Where you have calculated x, y and z to lie on the temporary axis.
There's a chance it will select the wrong axis, so check that the direction of it is correct.
Thanks for your reply, my question has solved.
Thansk a lot.