I claim the ornamental design for an stretcher bar frame, as shown and described.
FIG. 1 is a perspective view of a stretcher bar frame, showing my new design;
FIG. 2 is an enlarged front perspective view thereof;
FIG. 3 is a rear perspective view of FIG. 2;
FIG. 4 is a front elevational view of FIG. 2;
FIG. 5 is a rear elevational view of FIG. 2;
FIG. 6 is a top plan view of FIG. 2;
FIG. 7 is a bottom plan view of FIG. 2;
FIG. 8 is an enlarged left-side elevational view of FIG. 2; and,
FIG. 9 is an enlarged right-side elevational view of FIG. 2.
The broken lines in FIG. 1 depict environment and form no part of the claimed design. The additional broken lines shown in the figures represent portions of the stretcher bar frame, which form no part of the claimed design.