5 headphone jack. I was warned that Sena has a bad track record with backward compatibility, and its true. but came wrong size I was super careful to follow the instructions, because these aren?t that cheap and I didn?t want to mess up and waste any. If you have a wide foot then I dont think these are for you. 5, which is my regular size and they fit perfectly. It was a little tricky to install as I went side to side more times than I want to count as I tried to perfectly align the bars on my roof rails. Due to lack of space used as toilet roll holder and towel holder. It contains two parts, the unit itself which is quite thin and can be attached with screws to home made vertical panels, and a separate bracket for attaching the unit to a horizontal (such as desk) or vertical surface. Although I didnt find it necessary, I liked that the materials are already included in case the purchaser wishes to anchor the cabinet to the wall against which it will stand.