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I am going to be receiving some tennis racquets later today to shadowbox for one of my clients. I am wondering what is the best secure method to attach them down to the backing?
Two 1/2" straps of clear polyester film (aka Mylar-D) should provide good support for the racket. Run the ends through slots in a backer of fluted polypropylene (aka Coroplast) and secure them using polyester double-sided tape (NOT ATG). You can find lots of useful information in previous threads. Illustrated instructions are in the Complete Guide to Shadowboxes and Framing Objects.