High E Tuning Fork - 659 hz. John Walker tuning forks are known for their quality and superior performance. They produce a pure note (no overtones) with a sustain of 30-60 seconds to ensure accurate tuning. Perfect for choir leaders, conductors, cantors, music students and professional musicians. Tune pianos, guitars, banjos, harps or voice with the complete confidence that comes from using internationally recognized, ISO 9002 standard tuning forks.