A bench-top apparatus to determine the modulus of rigidity (G) of mild steel and verify the torsion equation. A circular MS rod is clamped between a fixed head and a loading head. Torque is applied via a lever arm + weights (or torque sensor), and the angle of twist (θ) is read on a protractor/encoder. From $T$, $\theta$, length $L$, and diameter $d$, students compute G, τ–γ curves, and discuss elastic vs. plastic behavior.

Parts Used:

1. Specimens: Mild steel solid rods (typ. $d=6-12$ mm, gauge $L=250-400$ mm)
2. Torsion Frame: Rigid base with fixed head and rotating loading head (self-aligning chucks)
3. Loading System: Lever arm with weight hanger (known arm length $l$) or torque sensor
4. Angle Measurement: Circular protractor + pointer or digital encoder/rotary potentiometer
5. Zero/Friction Balance: Light spring balance or counter-weight for initial zeroing
6. Instrumentation (optional): Digital tach/angle readout, data logger (Arduino/ESP32)
7. Accessories & Safety: Vernier caliper/micrometer, spirit level, guards, E-stop, weights set