The angle of inclined plane of a jack screw is also known as ______.

• A. Angle of Pitch
• B. Angle of Lead
• C. Angle of Thread
• D. Angle of Friction

Answer: (B)

The angle of incline for a jack screw is the lead angle. When the screw turns one full revolution, the nut rises by the lead L. The thread forms a helix around a cylinder, so the rise is L while the run around the circumference is pi times the mean diameter (pi d_m). The thread makes an angle with a plane perpendicular to the axis whose tangent is L/(pi d_m); that angle is the lead angle. This angle describes the effective incline the screw presents and sets the mechanical advantage and how much load you can lift per turn. If the screw has multiple starts, the lead is larger, increasing the lead angle and reducing the mechanical advantage. Other terms like pitch or thread angle describe different geometric features, and the friction angle relates to contact forces, not the incline of the screw.