If you wanna be cheap, leave an inch extra sitting on the insides of the helmet, duct tape that to the inside and make a nice duct taped inside, covers up the paint and resin fumes, or you could cut it to almost perfect size, leaving a ltitle off the edge and hot glue it in. I used industrial strength velcro just so when I wear one helmet I dont need to buy multiple visors, I can take a visor out of the helmet, put it into a new one easily and it fits perectly.