A simple spacer 21 mm rods

update versions
Version 2 for greater stability and replace retention ring
Version 3 to provide retention ring d = 8 D = 15
A simple rod spacer at 21 mm for Geeetech I3 pro b in case your current rod does not reach up

bom,
1 square nut m3
1 asparagus m3
1 bearing 608