Small Pulley Bearing Covers

These are covers that may be used to keep the string on pulley bearings used in a lift mechanism such as that available from REV Robotics (http://www.revrobotics.com/rev-41-1368/). They should work with similar bearings that have the following dimensions:

ID: 3mm
OD: 12mm
Width: 4mm

Small M3 washers should be placed between the bearing and the cover. For example: http://a.co/b0xFqGR