A while back, we recently launched some fuel fitting kits so you can make 5/16in fuel lines for Stromberg 97s. While the stock early Ford 1/4in OD hard lines are great-looking for a typical flathead motor, many people like the thicker lines for Chevys and other applications.
Regular Stromberg 97 inlet valves (needle & seats) were designed with a 1/4in pocket to take the fuel line and the angled seat is positioned so the brass ferrule can compress properly to seal on the 1/4in pipe. So you CANNOT use 5/16in OD hard line. If you do, the line does not sit deep enough into the fitting and, worse, as you can see in the picture below, it covers most of the ferrule sealing surface.
For 5/16in hard line, you need our 9564K-BIG S-jet inlet valves, which are designed specifically for 5/16in line, plus a pack of 9081K-BIG ‘Ford Nut’ style compression fittings. Assembly is then just the same as it would be for a regular 97 with 1/4in line.
FOR 5/16in hard line USE 9081K-BIG 5/16in Ford Nuts AND 9564K-BIG S-jets.
9564K-BIG S-jets also work with 9080K Superseat hose ends.
One more point. Do not use the Stromberg 9180K 1/4NPT hard line adapter for 5/16in tube into the 97 S-jet or needle & seat as the tapered NPT thread won’t fit or seal. The S-jet thread is 1/2in UNF.