Which pairing is correctly matched for color, size, and diameter?

• A. Red 4F 1.33 mm
• B. Gray 5F 2.0 mm
• C. Green 6F 1.67 mm
• D. Orange 7F 2.0 mm

Answer: (A)

In catheter sizing, the outer diameter in millimeters roughly equals the French size divided by 3. So 4F corresponds to about 1.33 mm (4/3 ≈ 1.333). The color often serves as a quick visual cue for the size, but the critical match is that the French size converts to that diameter.

The correct pairing is red with 4F and 1.33 mm because it exactly follows the F-to-mm conversion. The other options mix sizes and diameters that don’t align with the conversion: 5F should be about 1.67 mm, not 2.0 mm; 6F should be about 2.0 mm, not 1.67 mm; and 7F should be about 2.33 mm, not 2.0 mm.