🔍 Key Concepts

• Chordal addendum is a tooth height measured relative to the pitch circle using a chord across the tooth thickness. • On gear diagrams, the pitch circle is usually shown as a dashed arc, and the addendum is the part of the tooth that lies outside (above) this circle. • Look for a dimension that goes from the pitch circle up toward the tooth tip, not down toward the root or along the tooth flank.

💭 Think About

• Identify the pitch circle on the illustration first, then locate which labeled dimension shows the height from that circle toward the top of a single tooth using a straight (chordal) reference, not an arc. • Which of the labeled dimensions A, C, D, or L measures a radial height of the tooth above the pitch circle, instead of thickness along the pitch circle or depth into the root? • Ask yourself which label would be used by an inspector setting a gear tooth caliper to measure the tooth height above the pitch circle.

✅ Before You Answer

• Verify which line in the figure is the pitch circle and which is the outside (addendum) circle. • Confirm that the dimension you choose runs roughly radially (toward/away from the gear center), not tangentially along the circle. • Make sure the dimension represents the part of the tooth above the pitch circle (addendum), not the whole tooth depth or the dedendum (root area).