3.5mm is a pair of standard sized TRS jacks with flexible rear-panel headers. Hook your 3.5mm to any intellijel-format audio modules, like our "IO" to act as front panel inputs, outputs, or a combination of both! 3hp may seem like a strange width, but this was chosen for good reason - this was the minimum width the hardware fit inside, and when paired with another 3.5mm or a 1/4", you're left with an even number of hp occupied. Each 3.5mm also ships with a 1u1hp blank panel just in case! Width:3hp Depth:31mm (accounting for attached three pin cables) Passive power:+12v: N/A-12v: N/A+5v: N/A Our modules DO NOT include mounting screws! With the variety of preferences and sizes, we have decided not to provide mounting screws with our modules.