As everyone has already stated, yes, they are thinner. I have two, and confirmed it side X side with my American. I did find that my American J5 is lighter than either. I didn't weigh them, but I can easily feel the difference.
Human Base x.oc5, Warwick Corvette 5 Fretless, Fender Amer. Jazz 5, Squier Infinity 5 (x2).
Buying used strings is like buying used underwear.