2.5 , We do not recommend using it with phone cases that are too thick, as this may affect the stability of the connection. Full Audio Function : USB C to Lightning Audio Adapter allows you to connect your Lightning headphones to Type-C enabled devices to listen, make video calls and answer phone calls, as well as online controls such as music pause, music playback and volume adjustment through the function buttons on the headphones. NOTE: The adapter ONLY supports audio transfer, NOT charging or data transfer. Hi-Fi Sound Quality : Lightning to USB C Audio Adapter has built-in lossless decoding audio DAC chip that ensures stable audio signal transmission, supports bilateral insertion of lightning interface headphones, effectively filter current sound and noise, and better provides the original Hi-Fi sound, making voice calls clearer and bringing a sense of superior listening experience. Excellent Quality : The lightning to usb c headphone adapter adopts premium aluminum alloy shell