Foley catheters are human urinary balloon catheters. They are 45 cm long and the diameter varies from 12 French (1 French = 0.3 mm) to 24 French. A 20 French size is most commonly used in cows, while in heifers a 16 French is used. The balloon is distended with air or with flushing medium; ~15 cc in cows, ~12 cc in heifers.
Drost M (1984)