The adapter will allow you to continue using your old headphones. With 3.5mm headphone port on the iPhone 7 or iPhone 7+, one of your options will be a physical lightning to 3.5mm audio cable. You just plug your current earbuds or over-ear headphones into this cable and you're instantly streaming high-quality audio to your headphones.

IPhone 7 Lightning to 3.5 mm Headphone Jack Adapter. Support IOS 11.0.3

Specification : 
Material Cable : TPE 
Cable Length : 115mm
Material Adatper  : Alloy Alumimum
Adapter Color : Black, Silver, Gold, Rose Red 
DC Adapter size : 23.5*7.4mm
Lightning Adapter Size : 15.3x9.9x5.1mm
Color : Black, Silver

Technical Specification
Playback performance : 48KHz/16 Bit
Frequency Response : 20Hz - 20KHz
THD+N : < 0.01% at 3.3V 1KHz 0dBFS
SNT : -95dB at 3.3V
Working Current : 65mA Max at 3.3V
Working Voltage : 3.3V-5.0V, +/1 5%
Output : 20mW Max 16 ohm -1%THD