Foley's Catheter of size 16 F in French gauge system represents the measure:

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. 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