In a frame marking such as 50-18-140, what does the third number stand for?

• A. Temple length
• B. Eyewidth
• C. Bridge width
• D. Frame height

Answer: (A)

Sizing frames uses three measurements: eye size, bridge width, and temple length. In 50-18-140, the first number is the eye size—the horizontal width of each lens. The middle number is the bridge width—the distance between the lenses over the nose. The third number is the temple length—the length of the temple arm from the hinge to the end behind the ear. This temple length helps determine how far the frame sits behind the ears and how securely it fits, with common values around 135–150 mm. So the third number stands for temple length.