This adapter is designed to improve the comfort and durability of your Plantronics BackBeat PRO (1st generation) headset. It allows you to mount larger 120mm ear cushions, providing a more spacious and comfortable fit around the ears. This is particularly beneficial for users who spend many hours with the headset on, for example, at a stationary computer. By replacing the original ear cushions with larger alternatives via this adapter, you can potentially achieve improved wearing comfort and a more robust solution over time, compared to the standard ear cushions that often wear out quickly. The adapter is made to fit both sides of the headset.