A crucial part of the assembly is attaching the mouthpiece to the barrel. As with previous parts, push the mouthpiece into the barrel using a gentle twisting motion. When you are finished, hold the neck in front of you and make sure the flat part of the mouthpiece with the hole in it is facing downwards. This is where the reed fits on the mouthpiece. Since the reed rests against your bottom lip, it is essential that this part of the mouthpiece faces downwards.