After going to Home Depot twice, the first time being helped by someone who gave me the wrong item and the second time they just couldn't tell me what I needed, I finally went to Gorman Cooler Supply. It took about two minutes in and out and it cost me about $40 less, and it was the right item.
I made a note of this so when I need cooler parts or supplies in future that's where I'll go from now on.