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There are a lot of variables to consider. Most stores like Wal-mart (gardening section), Lowes, or Home Depot that sell window boxes include the necessary hardware, however many window boxes that are made by artisans may not include the screws and brackets. Also, you need to consider the size window you have. Measure the length of window you want to put a flower box before buying a flower box. Is there any wood along the window sill to attach screws to? You may need to get creative and sink some eye hooks into the wood and run thin cable to the window box. Make sure you keep in mind the weight of a fully watered plant and soil. Hope this helps!