What is the diameter in millimeters of a 4F sheath?

What is the diameter in millimeters of a 4F sheath?

• A. 1.33 mm
• B. 1.67 mm
• C. 2.0 mm
• D. 2.33 mm

Answer: (A)

The size in French (F) is tied to the outer diameter in millimeters, with 1 F equaling about 0.333 mm. So a 4F sheath has an outer diameter of 4 × 0.333 mm ≈ 1.332 mm, typically cited as 1.33 mm. This is the standard relationship used for sizing access sheaths. The other values correspond to larger French sizes (for example, 5F ≈ 1.67 mm, 6F ≈ 2.0 mm, 7F ≈ 2.33 mm), which is why they don’t fit the 4F designation.

The size in French (F) is tied to the outer diameter in millimeters, with 1 F equaling about 0.333 mm. So a 4F sheath has an outer diameter of 4 × 0.333 mm ≈ 1.332 mm, typically cited as 1.33 mm. This is the standard relationship used for sizing access sheaths. The other values correspond to larger French sizes (for example, 5F ≈ 1.67 mm, 6F ≈ 2.0 mm, 7F ≈ 2.33 mm), which is why they don’t fit the 4F designation.