Fuel thread pitch
 

What is the threading for the factory honda fuel filter? I'm trying to locate or fab a tee between the fuel filter and the fuel pressure gauge for my fuel input for my zex kit. I think it my be 1/8 npt, any input?

Its 12x1.25 on top and 14x1.5 on bottom. AEM lists the thread size in description on there site for direct replacement filter.

hmm, think i can find a tee at home depot to tee for a -3an fuel line?

They probably won't have metric threads at home depot

Plumbing flare fittings are flared at 45deg, an are 37deg. A JIC hydraulic fitting is the right thread and flare. Difference is they are steel instead of aluminum and the threads are cut slightly different. A farm supply store or somewhere that sells hydraulic parts should have them. Metric adaters would be harder to find then npt adapters, but you may get lucky.

You could cut the fuel hose and put a hose barb tee in it. 3/8 male barb on each side on 3/8 female tee in brass or black iron with 3/8 to 1/4 bushing for 1/4npt to 3/16 jic adapter.

Don't use galvanized fittings, the coating can flake off and clog injectors.
The brass is not alcohol compatible( 10% ethanol pump gas would be fine).
Black iron will get surface rust on outside after few months unless you paint it.

Or, this would get you a 1/8 npt to work with.
http://cgi.ebay.com/ebaymotors
/ws/eBayISAPI.dll?ViewItem&item=360152710099&viewitem=
Then you just need the -3an to 1/8 npt adapter
Zex Nitrous Oxide Systems NS6570 - Zex Nitrous Oxide Systems Fittings & Plugs - Overview - SummitRacing.com

ebay link doesn't work not sure why. search for honda fuel pressure gauge adapter on ebay it should come up.