A classroom exercise is described to introduce enzyme kinetics in an undergraduate biochemistry or chemistry course. The exercise is a simulation in which a student acts as an enzyme that "catalyzes" the unscrewing of a nut from a bolt. With other students assisting, the student enzyme carries out reactions with bolt-nut substrates under different conditions to illustrate limiting substrate, excess substrate, and inhibition. The class participates in collecting data and calculating reaction rates. Students use the results to construct a mathematical kinetic model for the simulated reaction. The constructed model parallels the Michaelis-Menten model for enzyme-catalyzed reactions that is presented in most biochemistry courses and textbooks. By using the simple everyday objects of nuts and bolts, this simulation enables students to directly visualize how reaction rates are measured and how they can be connected to mathematical models. In this way, fundamental concepts of enzyme kinetics can be developed before introducing more complex reactions catalyzed by molecular enzymes. (Contains 1 table.)