Mystery Head Bolt? in Dodge & Dodge Brothers Posted January 28, 2018 I have the 1939 original shop manual. It shows studs with nuts for the 8 cylinder and cap screws for the 6 cylinder. That's why these odd bolts/nuts are so odd. What makes it worse is that there are other pics online that show a mix of cap bolts and nuts, or the head-tapped cap bolts that some posters suggested earlier.