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
Foleys catheter 16 F means 
Select and explain. 
A. 16 mm inner diameter, B. 16 mm outer diameter, C. 16 mm circumference, D. 16 mm for 16 years old
B: 16 mm outer diameter
Answer: B: 16 mm outer diameter 
Explanation: 16 mm outer diameter