The IMPERIAL series has precision-round Imperial Crystal nylon treble strings in medium tension with the famous bass strings of the Classic series and differ in tension (black = low, gold = medium, red = medium, blue = high);Imperial Red medium/medium;(new gold packaging);Precision round Imperial Crystal treble strings in medium Tension;E1 medium: .0287"/0.73mm, tension 8.4kg/18.52lbs;B/B2 medium: .0327"/0.83mm, tension 6.18kg/13.62lbs;G3 medium: .0406"/1.03mm, tension 6.16kg/13.59lbs;Classic Red Bass strings in medium tension;D4 medium: .0295"/0.75mm, tension 7.21kg/15.89lbs;A5 medium: .035"/0.89mm, tension 6.93kg/15.27lbs;E6 medium: .0425"/1.08mm, tension 6.68kg/14.72lbs;