These are extra heavy, chromium-plated steel 440Hz tuning forks mounted on hardwood resonance boxes. This item serves as a combination tuning fork set that allows for two demonstrations. Without the weights, one fork responds to the vibrations of the other, illustrating sympathetic vibration at distances. With the weights, one fork can be tuned one or more cps different, and both, when struck, will produce beats of startling clarity. Rubber ball mallet included.