I think they're 1/4"

 

yes that's why to do it right you need a 5/16 to 1/4 hose barb adapter.

 

i went to home depot and they didnt have any 5/16 to 1/4 hose barbs. the guy said the plastic vacum line adapter should be safe. Do you use three brass fitting connecting them to get 5/16 to 1/4 or do they actually make that size?

 

Home Depot is a lumber company, not a hardware store. I did mine 9 years ago and I used 3 fittings. Recently in True Value hardware I noticed a new selection of brass hose barbs that cover just about any situation.