I think they are standard "tube nuts", but different size nuts for the front and rear ports (so you can't mix up). The tube sizes for both should be 3/16"D. The only other size I have ever seen is the 1/4"D tube from the MC in early cars w/ a single reservoir (~1966-). Don't ever install the wrong size tube, even if the nut on it fits the port. Always look at the size of the "inverted flare" inside the port. I have never bought tube nuts since I have a box of various brake lines from junkyard picks I can cut off and use. Any U.S. car up to ~2000 should work (almost all are 3/16"D tubing). After that, they started using "bubble flare" fittings.