The shelf measures 100 mm deep and 187 mm wide with small lips on all edges.  The screw holes are 5 mm in diameter.  I printed it in both PLA and PETG.  The PETG seems like it would hold more weight, but I would suggest putting anything very heavy on it due to the small mounting surface.  It is great though for smaller items and trinkets. 

Print with the side with the screw holes down with supports.