The Ring Roller is derived from IFUJI's "The circle roller":
http://www.thingiverse.com/thing:72655

The goal of this redesign was to make it easy to print.

Video: http://youtu.be/XwoA5oQFQ60

1. Print 2x RingRoller.
2. Remove the brims.
3. Push the rings together.

Printing settings:
; generated by Slic3r 0.9.9 on 2013-05-13 at 16:00:21

; layer_height = 0.25
; perimeters = 2
; top_solid_layers = 2
; bottom_solid_layers = 2
; fill_density = 0.4
; perimeter_speed = 40
; infill_speed = 60
; travel_speed = 180
; nozzle_diameter = 0.35
; filament_diameter = 1.75
; extrusion_multiplier = 0.8
; perimeters extrusion width = 0.39mm
; infill extrusion width = 0.39mm
; solid infill extrusion width = 0.39mm
; top infill extrusion width = 0.39mm

Brim = 3mm