(Blender Version 2.78a) it's a simple modeling of a stereo jack converter (3mm to 6mm) , the input seems to be not real size but it's because this is the outside and i didn't made the inside because it's not visible but i didn't use units like meters or imperial but i made the model with the rights proportions.You can use the model for whatever you want.

Note To Moderators:
My blender version was not in the choice so i picked up the last (2.77) but my version of Blender is 2.78a