They're 5/16"-18 X 3/4" (Coarse Thread). The thermostat housing will determine the bolt length. This measurement was for use with the OE aluminum housing. You may find it difficult to use a wrench on the lower bolt, if using a standard hex head type. I went with a "Button Head" stainless bolt. This takes an Allen wrench, which I found easier to use.
A forum community dedicated to Ford Mustang owners and enthusiasts. Come join the discussion about performance, builds, modifications, reviews, engine swaps, classifieds, troubleshooting, maintenance, and more!