3/8" inverted flare long throat. I was unable to find these fittings when I installed mine a year ago so just cut the line and spliced with hose. However, in the last week I was surfing for a cooler for my van and found a site that had similar fittings. See below. You'll have to contact them to see if they have 3/8".
http://www.drawtite-hitches.com/tran...cooler_acc.htm
http://www.bulkparts.com/MM001.ASP?pageno=1176
Might want to check Summit racing too.