fittings: NPT, BSP BSPT, 4AN etc etc etc....what do they all mean?!?!?!

[BlueShadow]

Hi guys, Ok so now that I'm actually buying turbo stuff for my car I figured it's time for me to learn what all these other terms mean. Dont laugh, this is what happens when your parents decide to put their kids in a Home Economics class instead of Auto Hobby. I dont even know where to start...I guess I just want to know what these fittings look like. I saw a pic of one when I did a search, and I believe it was a NPT to BSPT fitting. One end was a threaded inner, the other end was a threaded outer, I just wanna know for sure which one is which. I want to know what the common types of fittings and adapters I will need to be familiar with for connecting vacuum lines, fuel lines, and oil lines. TIA

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[VaporTrail]

hey, don't be ashamed, it's an intelligent question. I would like to answer but time does not permit me to answer

[mos]

National Pipe Tapered.
British Standard Pipe.
British Standard Pipe Tapered.
Army-Navy

All just different standards. The *PT fittings just have a threaded end, which is what seals. The AN fittings have a 37 degree conical end which is what makes the seal.

EDIT: If you see a hole, its a female end, if you see the outsides of the threads, its a male end. BPST and NPT are very similar, but they differ in two ways, the angle the threads are cut in are off by 5 degrees, also BPST has rounded thread peaks, while NPT has flat peaks. The O.D. and thread pitch are the same tho.




[Modified by mos, 12:30 PM 12/20/2002]

[BlueShadow]

National Pipe Tapered.
British Standard Pipe.
British Standard Pipe Tapered.
Army-Navy

All just different standards. The *PT fittings just have a threaded end, which is what seals. The AN fittings have a 37 degree conical end which is what makes the seal.

EDIT: If you see a hole, its a female end, if you see the outsides of the threads, its a male end. BPST and NPT are very similar, but they differ in two ways, the angle the threads are cut in are off by 5 degrees, also BPST has rounded thread peaks, while NPT has flat peaks. The O.D. and thread pitch are the same tho.


[Modified by mos, 12:30 PM 12/20/2002]

thanks, that helps out a lot...

So in this picture of a 3/8" N.P.T. to -6 AN, steel adapter fitting. the -6 AN is on the top because it has the tapered portion (37 degree) that makes the seal, and the bottom part is the 3/8" NPT, which have threads that go all the way to the end.

[Sonny]

Yeah, it is confusing as hell...Here's what I know so far:

BSPT is the thread pattern of the oil pressure sender switch that is located on the back side of the block. This is a common source for an oil feed line (using a T) for a turbo.

BSPT is not a common thread pattern in the US, but Honda used this on their block, so that's where all the adapter mess comes in.

NPT is very common in the US and most of the stuff that you buy here that is a brass pipe fitting is an NPT fitting. An NPT fitting is NOT tapered and requires teflon tape/paste for a good seal. Autometer gauges as well as most anything you buy for your car usually is an NPT fitting.

Most people install a BSPT to NPT thread adapter in the hole in the block and start from there. BSPT and NPT have the same thread pattern, but the BSPT hole is tapered. If your engine block is out of the car (like mine), you can just run an NPT tap through that BSPT hole (what I did) and then you have yourself an NPT hole that requires no adapter.

AN style fittings are what are used on steel braided lines. This is the hot ticket because these lines are pretty and they are very durable.

So, a typical turbo car might have something like this:

BSPT hole in the block with a BSPT-to-NPT adapter on it.
NPT-to-AN adapter installed inside the above adapter.

At this point, you basically have a -4 AN "nipple" sticking out your block.

You can run steel braided line up to a T that is on the firewall. The oil pressure sender plugs into one side of the T and then your oil feed line plugs into the other. Of course, it is not quite that simple. Most T's are NPT. So, your T ends up getting filled with adapters.

Confused yet??

Sonny

[xci_ed6]

don't forget flare variations on the brass fittings. I have to go to the hardware store 2-3 times for every fitting

-Dustin

[BlueShadow]

Yeah, it is confusing as hell...Here's what I know so far:

BSPT is the thread pattern of the oil pressure sender switch that is located on the back side of the block. This is a common source for an oil feed line (using a T) for a turbo.

BSPT is not a common thread pattern in the US, but Honda used this on their block, so that's where all the adapter mess comes in.

NPT is very common in the US and most of the stuff that you buy here that is a brass pipe fitting is an NPT fitting. An NPT fitting is NOT tapered and requires teflon tape/paste for a good seal. Autometer gauges as well as most anything you buy for your car usually is an NPT fitting.

Most people install a BSPT to NPT thread adapter in the hole in the block and start from there. BSPT and NPT have the same thread pattern, but the BSPT hole is tapered. If your engine block is out of the car (like mine), you can just run an NPT tap through that BSPT hole (what I did) and then you have yourself an NPT hole that requires no adapter.

AN style fittings are what are used on steel braided lines. This is the hot ticket because these lines are pretty and they are very durable.

So, a typical turbo car might have something like this:

BSPT hole in the block with a BSPT-to-NPT adapter on it.
NPT-to-AN adapter installed inside the above adapter.

At this point, you basically have a -4 AN "nipple" sticking out your block.

You can run steel braided line up to a T that is on the firewall. The oil pressure sender plugs into one side of the T and then your oil feed line plugs into the other. Of course, it is not quite that simple. Most T's are NPT. So, your T ends up getting filled with adapters.

Confused yet??

Sonny

Hmmm, actually I am starting to get an idea of how everything is supposed to hook up. I just want to see what you are talking about when you say the BSPT is tapered.

Do you also use AN fittings for vacuum lines? if not what would a typical vacuum connection look like from say the WG to the vacuum source? or where ever they hook up too.

[1.8T_EG]

... great info!!!

[tony1]

Just a note, NPT fittings ARE tapered and all pipe thread fittings require teflon tape or paste to seal.

[KOTSEMOTO]

This is a great thread. I wanted to build my own fuel line using the stock fuel tank. Some modifications will be made at the pump side. But What i'm thinking is if I could use a stainless steel hard line to connect SS braided hoses. It would be expensive to go Briaded hoses all the way so I'm planning on a stainless steel hard line underneath the car. Will a -8 AN be enough or 400HP?

[Sonny]

Just a note, NPT fittings ARE tapered and all pipe thread fittings require teflon tape or paste to seal.

Tony,

Are you saying that there is taper in these NPT to AN fittings?



If there is, I sure don't see it...or are you talking about right at the very tip of the threads?

As far as BSPT, I thought it was the taper (very noticeable with the OEM oil pressure sender) is what gave it the seal? When I removed the sender from the block, there was no tape on it...do they use a paste at the factory?

Thanks,
Sonny

[earl]

All npt fittings are tapered. They start smaller and get larger. They do not bottom out. They basically just stop turning when the thread diameter becomes too large. Teflon tape and pressure makes them seal.

[mos]

Just a note, NPT fittings ARE tapered and all pipe thread fittings require teflon tape or paste to seal.

Well ya, the T in NPT stands for Tapered. So it'd be a "NP" thread without the taper. And I agree that you should use some type of teflon sealant with NPT threads even though they are tapered.

The taper tends to be less pronounced in the higher quality fittings, and much more noticable in the cheap stuff, like you will find at home depot. With the cheap stuff you can sometimes only get a few threads in before the connection refuses to tighten any more.

The threads are what taper out towards the base of the fitting, the fitting itself is not tapered. You will probably want to avoid any fitting with a flare in it (NPTF fittings). As somebody already mentioned, Home Depot sometimes has these instead of the plain NPT fittings. It will vary by location.

The whole reason you need to go AN and use those pesky adapters is that they swivel. If you had your whole hose system made up of NPT ends, you would have no way of tightening up the ends. As you turn the end, the whole hose would turn, and unscrew the other end.

[SiRkid]

awesome post.
who use's teflon with their adapters in the turbo?

[Sonny]

Good info, guys. Thanks.

Sonny

[Pat]

wow, I was just gonna ask this question too!

1 question I have:
Do the size numbers like, -4 , indicate an actual measurement or just a standardized size number and does the - in front of the number represent anything or is it just the semantics they chose?

[AbaZ]

Since NPT fittings are Tapered you are not even suppose to use Teflon tape or any type of sealer. Most nut/bolt/hardware stores will tell you the exact same thing. But personally what I have done in the past, is just use 1/8 NPT on the back of the block with some Teflon tape, it works fine, and it doesn’t leak. Don’t over tighten it, bass is very soft.

Jeff Frank

[AbaZ]

I could be entirely wrong, but I thought it was a measurement, meaning

-an 6 would be 6mm's? it looks about right, but like I said, just a guess

Jeff

[mos]

AN goes by sixteenths. So -4 would be 4/16", and so on. From the documentation from my fitting supplier you are supposed to use some kind of sealant even with tapered fittings.

[tony1]

Since NPT fittings are Tapered you are not even suppose to use Teflon tape or any type of sealer. Most nut/bolt/hardware stores will tell you the exact same thing. But personally what I have done in the past, is just use 1/8 NPT on the back of the block with some Teflon tape, it works fine, and it doesn’t leak. Don’t over tighten it, bass is very soft.

Jeff Frank

You ARE supposed to use teflon sealant on all pipe thread fittings. Don't believe what the idiot that works at the hardware store tells you...

[BlueShadow]

Hey Guys,

thanks for all the info, I'm learning quite a bit, but I have another silly question that I had to ask.

what is a banjo bolt? what does it look like, and where are the common places that you will use them?

thanks

[BlueShadow]

Hey again,

Also I came upon this pic while doing a search...is this what a typical oil drain setup looks like?

With the oil drain line all that has to be done is a -8 line needs to be ran from the turbo drain(right side of pic) and the other end gets tapped into the oil pan right (left side of pic)?

pic courtesy of TurboHatch

[B18EG6]

The banjo bolt is the type of bolt on the top of your fuel rail. It is a fitting for the end of a hose, kinda like a ring. You screw a bolt through it, onto the fuel rail, and there is a hole in the screw which permits fluid to flow through it. lemme find a pic...


heres the hose end...



I cant seem to find a pic of the BOLT anymore, imagine a bolt with a hole down the axis of it, and then another small hole perpendicular to the axis so the fluid can flow through it.


Edited on 08.03.03


Modified by B18EG6 at 8:05 PM 8/3/2003

[BlueShadow]

Hi,

I have yet another question, on the pic below is "A" the connection that I will be messing with to hook up my oil pressure guage? If I'm using an electrical oil pressure guage (in cabin) how do I go about getting it hooked up?

TIA

pic courtesy of Arturbo

[B18EG6]

"a" is the stock oil pressure sender. See where it says "to gauge"? on that side of the tee is where you screw in the electrical oil pressure sender for your aftermarket gauge.