The Head Adaptive Tuning Kit also you to customize your Graphene Touch Instinct Adaptive tennis racquets to your preference. You can choose between the more open 16x16 string pattern if you re looking for massive spin or you can take a more traditional approach and keep the 16x19 grommets in. Not only can you select the string pattern but you can select between lightweight and heavy grommets to help increase the stability of the racquet. The kit also comes with handle spacers that allow you to extend the racquet in 5mm increments (5mm 10mm or 15mm). The last feature of the kit is a weighted butt cap insert that allows you to add 10 grams of weight to the tail-end of the racquet. This Kit comes with: 3 Grommet Sets Heavy 16/19 (adds 5 grams / 0.18 oz) Light 16/16 (no additional weight) Heavy 16/16 (adds 5 grams / 0.18 oz) 3 Spacer Rings +5mm (adds 0.2in / .5 cm) +10mm (adds 0.4in / 1 0 cm) +15mm (adds 0.6in / 1.5 cm) 1 Butt Cap Heavy Butt Cap (adds 10 grams / 0.35 oz)