Ok I have a gauge I was planning on installing in my rail. I have a 90 degree fitting to bolt the gauge to         my question is     what size are the damn threads? All I know is that the gauge will thread into "Any 1/8" NPT fitting". What is NPT? I am totally lost here      any help would be greatly appreciated.
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2003 Cavalier LS Sport "SHOCKWAVE"
 
NPT = National Pipe Thread.
  
 
 
ok so how can i figure out what type of thread it is 1/8"  by what?
We Ride Together, We Die Together...... J-Bodies For Life!
SPONSORED BY: Showstopper Tuning, JM Graphics
2003 Cavalier LS Sport "SHOCKWAVE"
 
Not 1/8" by anything... a 1/8" NPT is its own size.
 
 
oh ok then    so where can i find a tap to thread my fuel rail?   i tried home depot and 2 local hardware stores all had nothing
We Ride Together, We Die Together...... J-Bodies For Life!
SPONSORED BY: Showstopper Tuning, JM Graphics
2003 Cavalier LS Sport "SHOCKWAVE"
 
You can get a brass adapter to go from your fuel rail size to 1/8"NPT female.  Its far cheaper and less hassle than a tap.
I don't know the thread size, so can't help there.
 
 
i found a tap at the local fastener place    problem solved
We Ride Together, We Die Together...... J-Bodies For Life!
SPONSORED BY: Showstopper Tuning, JM Graphics
2003 Cavalier LS Sport "SHOCKWAVE"