binding a screw on axle

[iron72]

Hello.
I created a detail that has a circular asola, inside it has to pass a screw.
in assembly I would like to bind the screw axis to the circular axle as I can do?
I tried to build another sketch on the asola to create a semicircle that passes on the axis of the asola and leave it visible in the assembly for a possible bond that I can not get.
see photos:

 

[iron72]

Then I finally got rid of an offset, the radius of the axis of the circular axle, with the axis of the screw.

 

[falonef]

with the right button you should be able to select the virtuasle axis of the asola. search under the voice other selections (it seems in Italian)