When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
I believe they are 1/4". I ran mine the the port on the radiator. I used a Camaro radiator in my 93 Mustang. Some have drilled and tapped the top of the water pump.