What's a "double-stop"??

Good explanation Az. I just don't think of power-chords or intervals as being capable of being inversions. Personal preference. Just because if you invert a interval it becomes a different interval. Like E5 or an E power-chord becomes Bsus4. A sus4 is often thought of as a chord, but the 5th is optional and the 3rd isn't usually played harmonically with the chord, instead it's played like a neighboring tone. So the harmonic chord you end up with is a perfect 4th interval. Just in case someone was wondering about that.