To upgrade or downgrade the lining of your Arai helmet, you can order the lining in different strengths. To know the strength of your actual lining, please have a look on the label which is fastened on the lining in your helmet. Suitable for Arai Tour-X 4 Arai MX-V Arai MX-V EVO Features Lining (100% polyester) easily cleaned Head circumference in cm Helmet size Lining Typ Tighten Standard Looser 54 XS II 12 mm 10 mm 7 mm 5 mm 55-56 S II 12 mm 10 mm 7 mm 5 mm 57-58 M III 12 mm 10 mm 7 mm 5 mm 59-60 L III 12 mm 10 mm 7 mm 5 mm 61-62 XL IV 12 mm 10 mm 7 mm 5 mm 63-64 XXL IV 10 mm 7 mm 5 mm