What Is On The Outside Of A Fire Hydrant?

Riddle: If a fire hydrant has H2O inside, what does it have on the outside?

Answer: K9P (you'll get it eventually).

Source: https://www.riddles.com/index.php/81

If a fire hydrant has H2O inside, what does it have on the outside? — What is on the outside of a fire hydrant? by Anonymous v1.

Riddle: If a fire hydrant has H2O inside, what does it have on the outside? Answer: K9P (you'll get it eventually). — by Anonymous v2.