By this arrangement we ensure that spindle can rotate freely once the outer nut is tightened to the main body.
After that inserted the cap on the spindle so that the square male protrusion on the cap fits in its counterpart on the spindle .Then permanent connection is ensured by the help of screw. There are threads only on lower part of the spindle thus ensuring good connection between them.
Slide the valve disc on the groove on the lower portion of the tap.
Finally tighten the outernut on the tap.Ensure that they are tightly fitted so that this should not open by any means when the tap is operated. Though the clearence between the outernut and the spindle cover ensure this but other elaborate alternatives should also have to be ensured.
Now tighten the cap to lower the valve disc over the seat on the main body.