This set of 12 steel extension springs features looped ends in a range of sizes for comparative physics experiments. The set includes pairs at six different size combinations: 9 x 1.25 inches, 9 x 0.75 inches, 9 x 0.4 inches, 8 x 0.6 inches, 6 x 0.9 inches, and 6 x 0.75 inches (length x diameter, two of each). The variety of spring constants allows students to investigate Hooke's law, potential energy storage, mass-spring oscillation periods, and damped harmonic motion. The looped ends allow easy attachment to hooks, masses, and other apparatus. Made from quality steel with sturdy construction for long-term classroom use.