This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Anaesthesia
Foley's Catheter of size 16 F means? 
Select and explain. 
A. 16 mm diameter at the tip, B. 16 mm inner diameter, C. 16 mm outer diameter, D. 16 mm circumference
D: 16 mm circumference
Answer: D: 16 mm circumference 
Explanation: 16 mm circumference REF: SRB's Manual of Surgery by Bhat - page 625 The French scale or French gauge system is commonly used to measure the size (outside diameter) of a catheter. It is most often abbreted as Fr, but can often abbreted as FR or F. 1 Fr = 0.33 mm, and therefore the diameter of the catheter in millimeters can be determined by dividing the French size by 3. And since circumference is equal to the one third of diameter, catheter size of 16 F means 16 mm in diameter. Also know: Foley's catheter is sterilized by gamma radiation Usually Foley's catheter is kept for 7 days Size: Adults-- 16 F Children-- 8 F or 10 F