Head Adaptive Tuning Kit, you can customize Adaptive Instinct racquet to meet your exact needs. This kit not only allows you to add a spin friendly 16x16 string pattern to your Adaptive Instinct racquet, but it also give you the ability to select from differently weighted side grommets so that you can fine tune your racquet's maneuverability and stability. This kit also comes with handle spacers so that you can extend the length of your racquet by 5mm, 10mm or 15mm. Lastly this kit gives you the ability to tail-weight your racquet with a heavy butt cap insert.