Brass, Copper, Iron 25mm diameter pendulum bobs with hooks Approximate weights: Brass - 2.1oz, Iron - 2.44 oz., Copper - 2oz Brass hook on bob is threaded and removable Great for studying a variety of physics experiments, motion, oscillations, simple harmonic oscillators Works well with Eisco pendulum clamp PH0308 The pendulum bob provides one of the necessary tools for studying the physics of pendulum motion (tension force, gravity force, centripetal force, potential energy, kinetic energy, etc.). When used with a full pendulum set up, it provides a visually and kinesthetically effective method by which to study pendulum physics.