The audio adapter is designed for the HTC One Max:

• HTC One Max

If you have any of the above model of phones, before you use a standard hands free headset with your HTC One Max cell phone, you will need to plug in the 2.5mm audio adapter in order for the headset to work. Just plug this audio adapter into your cell phone to convert the audio. This adapter allows you to use a 2.5 headset with your HTC One Max phone.

• Easily installs; simply plug the audio adapter into your HTC One Max cell phone audio jack; then plug in any 2.5mm, two ring headset into the audio adapter
• One year warranty
• Made by HTC