FIG. 1 is a perspective view of a speed reducer for retractable screen systems illustrating my new design;
FIG. 2 is an enlarged perspective view of a speed reducer of FIG. 1;
FIG. 3 is an enlarged front elevational view thereof, the undisclosed rear view being identical;
FIG. 4 is an enlarged right side elevational view thereof, the undisclosed left side view being identical;
FIG. 5 is an enlarged top plan view thereof; and,
FIG. 6 is an enlarged bottom plan view thereof.
The broken line showing of a retractable screen in FIG. 1 is for illustrative purposes only and forms no part of the claimed design.