Photo of STIX flight-spare front (left) and rear (center) grids, mounted in their grid support frames. The front grid assembly is seen from the Sun side, while the rear grid is seen from the detector side (so that for window comparisons, one should mentally “flip” the rear grid). The numbers indicate subcollimator labels (similar colors correspond to grids that were etched on the same foils). The blue circles indicate the locations of fiducials, used for optical characterization and grid-to-grid alignment. Individual windows are 22 × 20 mm (front) and 13 × 13 mm (rear). On the right, a back-illuminated picture of a front grid on top of a rear grid is shown to highlight the created Moire patterns. This Moire picture uses an early prototype grid with different assignment of the individual windows.