The Green Knobby Tube offers increased sensory input from the raised bumps along the bitable stem. It provides a slightly firmer bitable surface than the Chewy Tubes. The Green Knobby Tube features a stem of 9/16″ outside diameter (OD). Green, bumpy, T-shaped, tubular For chewing and biting skills, TMJ stimulation, oral exploration… Reusable, durable and easy to clean Non-toxic, FDA compliant, free of latex, lead, PVC and phthalates