I went on NAPA Auto Parts web site and started poking in old Cars at random until I found what I was looking for...their website lists the bore size. I was working on a Nova with Wilwood brakes but ended up using the master from a 68-72 corvette I think it was...It has a 1 inch bore...it was made for 4 wheel disc brakes but as long as you instal a risidual valve between it and the rear drums it will work...I didn't need one for some eason but have only ran it once so far.