I am just about done putting these blasters together for my kids and I discovered that I am missing something on the front sprocket. I received the new sprockets and chain in the mail, everything went together fine except, how does the front sprocket get locked onto the shaft? I am obviously missing the front sprocket holder and the two screws. Once I order and receive the front sprocket holder and put it on, the screws go into the sprocket but what holds the sprocket and holder onto the shaft? Is there something else I will need as well?