is anyone familiar with the akg k550 headphones? i was wondering how they terminate, in a 3.5mm end or one fourth inch end? it says something abour 3.5 mm to 6.3mm but i didn't know what to make of this. thanks, john
The 6.3 mm is a rounded-off value in metric system for 1/4-inch in the English system. The conversion is 25.4 mm per inch. That would be 6.35 mm plug.
It's possible that the value is intentionally 6.3 mm instead of 6.35mm to provide some clearance for insertion into the jack. My AKG K140 (old!) headphones has the 1/4-in jack standard, and it measures 6.3 mm plug diameter.
The AKG has BOTH sizes. there's an included adapter so you can use either jack size.