Frey Scientific Sympathetic-Differential Fork Set contains a combination of tuning forks that allows two demonstrations: one with weights and other without weights. Extra heavy chrome-plated steel forks each measure 1-1/4 inches ( or 32 millimeters) wide. Both are mounted on hardwood resonators; mallet included. Features Sympathetic Differential Forks. This combination tuning fork set allows for 2 different vibrancy demonstrations for comparing and contrasting. Without the weight, one fork responds to the vibrations of the other and demonstrates sympathetic vibration at some distance. With the weights, one fork can be tuned 1 or more cps different. When both forks are struck with mallet weight, it will produce beats of startling clarity. Extra-heavy chrome-plated steel forks are mounted in hardwood resonators and come with mallet for instant use. Includes: One Combination Tuning Fork Set ( with 2 Forks, Mallet, and Mounted Bases). Specifications Country of Origin: India. Safety: No Choking Hazard. Allergens: Contains No Allergens. Material: Chrome Plated Steel.