hi guys i am in the process of drilling and tapping for the pyro and boost gauge and have some questions....

1. the fittings on both the pyro/boost are labelled as 1/8 npt,
at the risk of looking foolish, what does this mean? the 1/8"
does not seem to measure in anywhere as opposed to other
bolt or tap sizes, and what does npt stand for. I do have a npt
27 tap which looks like the right size.......Iam installing the auto
meter phantom gauges.

2. if the npt 27 tap is the right tap to use, what is the proper drill
bit size.....ie, how much smaller to you go.

 

I don't know what "npt" stands for (I think it is a plumming term), or why they call it 1/8", but I do know the characteristics. NPT types have a taper to them that creates a seal when tighten. Before you do any drilling, make sure you have the correct tap and drill size. I went to Ace an bought the tap and bit just for that operation. It never hurts to start out with a sharp bit!

 

NPT = national pipe thread I think? your NPT 27 may be a 1/8" NPT which has a pitch or thread count of 27. I think a remeber a 27 tamped on the side of my tap too...I will go look. Test drill/tap some scrap and see if it is correct. Fool proof.

 

1/8 NPT is a very common size. NPT stands for national pipe thread, the 27 you have will be the right tap, I believe the 1/8 comes from measuring the ID of a piece of pipe can't remember what spec though. 27 is the number of threads per inch. HTH

 

triplenickel is spot on!