Composite multifilament (KF) core — gut-like warmth and focus with laser-quality manufacturing. Fast response at every dynamic. 4/4 size, medium gauge.  Strings should generally be changed every 6–12 months, though students usually change them less frequently. Even if strings haven't broken, they gradually lose their brilliance and responsiveness — if your instrument sounds dull or takes longer to settle in tune, it's time for a fresh set.