My Bose QC 35 headphones have a 2.5mm socket but on the headphones end for when you'd want to use them wired. It came with a cable with a 3.5mm male plug for th

My Bose QC 35 headphones have a 2.5mm socket but on the headphones end for when you'd want to use them wired. It came with a cable with a 3.5mm male plug for the source device and the 2.5mm male plug on the side that goes to the headphones. Never seen a wired headset with 2.5mm male plug that goes to the source device however.