Plantronics Snap On Behind the Head Neckband for Wireless Headsets is compatible with CS540, W740, W740-M, W440 and W440-M wireless headsets. It offers fantastic alternative to a traditional headband that goes over the top of the head and it is ideal for those who desire to eliminate the constant pressure of a headband or earloop around the ear. It is made out of tough nylon material, super lightweight, flexible and durable. It comes with smokey gray high-tech color that blends away from view (you can barely see it when worn). Adjusting connectors will make a perfect fit fir everyone possible. It is compatible for both ears.