[quote name='bassman7755' timestamp='1396639986' post='2416037']
Tension is a function of pitch, length and mass. Those are the only variables so given that pitch and length are fixed, in order to get a lower tension you need a string with less mass. The most obvious way to do that is to use a lighter gauge ..
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Possibly a bit more to it than that. Tension is mainly carried by the core, so a narrower core with chunkier windings can have the same mass as, but less tension than, a string of the same external gauge.