Salter Labs Concentrator Humidifier Adapter Tubing 21", Three Channel Safety Oxygen Supply Tube, with One Molded Ribbed Connector End and One Male Thread Grip EndSuperior safety due to crush-resistant internal wall design...a Salter innovation Special design features three inside channels that help prevent accidental occlusion. A unique "ribbed body" end fitting allows easy connections. Available in lengths from 4 ft to 100 ft. Thread grip, male or female ends are Special or custom lengths available with minimum one case order. A selection of smooth bore tubing is also available.Crush resistant, three-channel safety design.Green or clear “no memory” tubing.Innovative connector design has ribbed end piece with rounded, tapered edgesAttaches easily to fittings.