This is a adapter for bushings, eg. broncebearing.
I've paused the print at 19.75mm and inserted the broncebushings, then resumed printing.
I used http://prusaprinters.org/color-print/ for that.

make a few tests while adjusting the inner diameter of the adapter, be sure the inserted bushing fits in tight!

Print instructions

Pause print at 19.750mm (better check the height in your slicer!), insert bushing and resume printing.