Teether Bite Stick Chewing Tube Sensory Chew Biting Aid Oral Muscle Training The Yellow Chewing Tube offers a smaller stem size for chewing and can also be used with an individual who cannot open the jaw very wide. The Yellow Chewing Tube features a narrow stem 9.5mm OD. The Red Chewing Tube offers a slightly wider stem 12.7 mm OD. This tube can also be used by children who are receptive to oral tactile stimulation or with adults who have a larger jaw. The Green Chewing Tube has been designed to increase sensory input by means of the raised dots on the shaft. The shaft diameter is 15mm OD. The Blue Chewing Tube is intended for adolescent or adult size jaw.It is the largest and firmest of the Tubes. Adults with developmental disabilities and adolescent with autism or sensory integration disorders may wish to use this larger size. Note : Chewing Tubes are not recommended for use with children under 7 months of age.