Thread sizes???

Submitted: Tuesday, Apr 12, 2005 at 17:54
ThreadID: 22006 Views:5488 Replies:8 FollowUps:18
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I'm just in the process of working out an order to place with VDO for some gauges and associated sender units. I know from bitter experience with my oil pressure sender unit, that Nissan engines do not have NPBT threads. I am going to order a coolant temp gauge and sender with 1/8" NPBT thread. I can also order a small brass adaptor with this thread on it's inside diameter and I have a choice of M14, M16 and M18 outside threads to choose from. I want to instal the sender at the top of the thermostat housing, near the position of OE sender unit. I have 2 choices: there is a hex bolt which is just filling a hole and there is also another brass fitting with a barb on it which points upwards at about 45 degrees and has a rubber stopper over it's end. It seems as though it was intended to have a hose going off to another part of the motor, but Mr Nissan decided that it wasn't needed on the Australian model.
Now, finally, to my question......how do I measure the size of the threads in the fitting/s when I remove them? I have a micrometer and can measure the diameter of the thread either on the outside of the thread or in the groove of the thread. I believe the M14 relates to 14mm diameter, but not sure where this measurement is taken from?
Any engineers out there who can enlighten me please?
Thanks in advance blokes
Cheers
Roachie
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Reply By: GOB & denny vic member - Tuesday, Apr 12, 2005 at 18:03

Tuesday, Apr 12, 2005 at 18:03
goodday roachie
wolfie might be your man to contact if it was me i get bolts and try them till i find a matching size

steve
AnswerID: 106388

Follow Up By: Exploder - Tuesday, Apr 12, 2005 at 18:46

Tuesday, Apr 12, 2005 at 18:46
It’s the outside Roachie.
M14 is the major diameter of the thread,
The inside will give u the minor diameter.
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Follow Up By: Member - Roachie (SA) - Tuesday, Apr 12, 2005 at 22:17

Tuesday, Apr 12, 2005 at 22:17
Thanks Steve and Exploder.....
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Reply By: Vinnie - Tuesday, Apr 12, 2005 at 18:39

Tuesday, Apr 12, 2005 at 18:39
Roachie

The size of any metric screw or bolt is the diameter of the thread overall

As for the thread - it is measured TPI (Threads Per Inch) - I know it`s metric you say.

Metric threads are either Course or Fine.

In 99% of vehicle manufacture that use metric fixings the thread will be Fine

A thread gauge will identify TPI

Hope this may help

Vinnie
AnswerID: 106393

Follow Up By: Nudenut - Tuesday, Apr 12, 2005 at 18:55

Tuesday, Apr 12, 2005 at 18:55
and then theres european metric and australian or was that japanese...two of them are different pitch if I recall correctly..or am i thinking of somthing else?
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Follow Up By: Nudenut - Tuesday, Apr 12, 2005 at 18:58

Tuesday, Apr 12, 2005 at 18:58
and if its metric, it cant be measured in tpi..can it?
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Follow Up By: Jim-Bob - Tuesday, Apr 12, 2005 at 19:34

Tuesday, Apr 12, 2005 at 19:34
G'day Vinnie
Your right in saying that you measure the O.D. of any thread but as far as metric threads are concerned you dont use TPI, you measure the pitch of the thread in millimetres, I.E. 1mm, 1.25mm, 1.5mm and so on.
Thread guages are either imperial (T.P.I.) or metric (parts of mm's), two different sets.

Safe travells.
Jim-Bob.
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FollowupID: 363424

Follow Up By: Member - Roachie (SA) - Tuesday, Apr 12, 2005 at 22:21

Tuesday, Apr 12, 2005 at 22:21
Thanks for your valued input blokes, I pulled out the largish hex head bolt after work and the thread size is considerably smaller than the head would indicate.....ie: it's about a 15mm hex head and about a 1/8th bsp thread.
Back to the drawing board.......lol
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Reply By: dirtdodger - Tuesday, Apr 12, 2005 at 18:45

Tuesday, Apr 12, 2005 at 18:45
Hi Roachie, I assume that your engine is a petrol. The hex bolt on the thermostat housing, if it is the one just forward of the normal temp sender, on the diesel is the mounting point for the glow plugs circuit temp sensor. This is a parallel metric thread of approx 10 mm coarse.... very close to 1/4 NPBT.

I have used this point to tap 1/4 NPBT threads, then use a 1/8-1/4 adapter to fit the normal aftermarket 1/8th sender unit........plenty of metal in that spot and works ok with no leaks, and temp sensing is in the correct spot.
AnswerID: 106394

Follow Up By: Member - Roachie (SA) - Tuesday, Apr 12, 2005 at 22:24

Tuesday, Apr 12, 2005 at 22:24
Mate, mine is a 4.2 diesel, not petrol. There are 3 threaded holes in this area. 2 of them have fittings in them....one (middle) is obviously the temp sender, was unsure about the rear one, but you may well be right about it having something to do with glow-plug sensor....and the other one (front, closest to the radiator) is the hex bolt which just fills an unused hole.
Thanks
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FollowupID: 363461

Reply By: warthog - Tuesday, Apr 12, 2005 at 20:28

Tuesday, Apr 12, 2005 at 20:28
Hi Roachie,
Sorry I don't know how to measure threads but am also interested to find out. What I am wondering is where are you going to put your guages in your gu. Also have found outerlimits4x4.com a good place for tech questions, alot of heavily modified vehicles on that site.
AnswerID: 106421

Follow Up By: warthog - Tuesday, Apr 12, 2005 at 20:31

Tuesday, Apr 12, 2005 at 20:31
If I had of read the replies before making my post I would have already been enlightened on thread sizes
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Follow Up By: Member - Roachie (SA) - Tuesday, Apr 12, 2005 at 22:31

Tuesday, Apr 12, 2005 at 22:31
Thanks mate, I might check out outerlimits or the patrol forum.
As for the gauges.....I have a Dept of Interior dashpod which already has lots of stuff (UHF + separate speaker + voltmeter). But, on the driver's side of it I have already attached a small 90deg bracket and mounted a VDO oil pressure gauge. So all I need to do is remove the black base which only holds one x 52mm gauge and fit one that holds 3 x gauges. The right hand side of the longer bracket will have to have a bolt inserted which I will be able to adjust so that it supports that end by resting on the dashcarpet. I will still have one gauge to fit (the boost gauge would be the obvious choice), which I will try to mount high up on the A pillar. I already have an air pressure gauge (for my air tanks) mounted on the A pillar using the lower screw that holds the grab handle; so the other gauge will be attached using the upper screw.
Cheers
Roachie
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Follow Up By: warthog - Tuesday, Apr 12, 2005 at 22:54

Tuesday, Apr 12, 2005 at 22:54
Thanks, that sounds like a good placement.As far as aftermarket guages go I only have a pyrometer,mainly due to funds and placement issues. It is mounted in a VDO dash pod (#230029 I think) that is screwed into the plastic trim on the A pillar down near the dash. It's adjustable for angle so looks ok and is easy to see
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Follow Up By: BenSpoon - Wednesday, Apr 13, 2005 at 16:17

Wednesday, Apr 13, 2005 at 16:17
Warthog- How much did the A-pillar pod set you back? I've been having a pig of a time trying to track down a 2 or 3-gauge A-pillar pod- no one can find them for me!
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FollowupID: 363546

Follow Up By: warthog - Wednesday, Apr 13, 2005 at 21:46

Wednesday, Apr 13, 2005 at 21:46
$40 from repco, only holds one guage though. Bloke who sold it to me knocked it down from retail a bit. There is a pic of it in the vdo catologue that can be downloaded from vdo web site,
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Reply By: Stew53 - Tuesday, Apr 12, 2005 at 20:43

Tuesday, Apr 12, 2005 at 20:43
Roachie
A lot of Japanese equipment use BSP on their tapered threads on their cooling systems and sender units, probably goes back to the early days of copying British cars etc. Pirtek and Enzed used to have thread identification booklets available or may be able to identify the thread for you if you take it down to them. BSP and NPT threads are not measured on the outside of the thread they are sized according to the inside diameter of the pipe so it gets a bit confusing, I have noticed the blanked off fitting on the Nissan months back and at the time I thought it would be a good take off point for a coolant filter, I suspect that it is 3/8" BSP.
Most people would not concider BSP as the car is Japanese and must be metric.
Stew
AnswerID: 106424

Follow Up By: Michael ( Moss Vale NSW) - Tuesday, Apr 12, 2005 at 21:07

Tuesday, Apr 12, 2005 at 21:07
Well its all happening on this thread..(no pun intended) Stew53 is on the right track.. Roachie if its a pipe thread on a Nissan it is BSP(british standard pipe) not NPT, thats american (National pipe thread). You can actually screw many of the NPT and BSP threads into each other so dont be fooled, the thread pitch is slightly different and may leak, also may damage the threads in the engine. BSP is the go!!! Michael
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Follow Up By: Exploder - Tuesday, Apr 12, 2005 at 21:14

Tuesday, Apr 12, 2005 at 21:14
OK. Didn’t know they had B.S.P threads on them.
If it is 3/8 the size is as followed for B.S.P (British standard pipe)
3/8=TPI 19
Major Diameter 0.656in
Minor Diameter 0.5886in
Depth of Thread 0.0337in

And if you need to tap it the tap drill size is 14.75mm
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Follow Up By: Member - Ed. C.- Tuesday, Apr 12, 2005 at 21:54

Tuesday, Apr 12, 2005 at 21:54
Well, I've come in a bit late on this one, & was just gunna chuck in my 2-bobs worth, but the response & follow-up above pretty much sum up what I was gunna say....
I will however, elaborate....
There's pipe threads, and there's pipe threads....
In this particular case, it would be BSPT (British Standard Pipe Tapered)... This is a "sealing" thread, though ya still need to use a sealing compound...
BSPP (British Standard Pipe Parallel) is I believe, the standard for gas fittings, and is a "joining" thread, the sealing being accomplished by ferrules, or tapered fittings (not the thread itself)...

Further, BSP threads have a 55deg. pitch, while NPT (National Pipe Tapered) threads have a 60deg. pitch.... TPI (Threads Per Inch) is also different with each size... As mentioned, NPT is the American standard, & not so common here....

While I'm here... Roachie, I believe that barb fitting (with the rubber cap on it) in the thermostat housing cover is in fact an air bleed... you're s'posed to remove that (the cap) when refilling the rad. after emptying/flushing.. lets the air outa the system... You'll find that there is another of these in the heater hose near the firewall....

Catch ya later... Ed. C.

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"He who lie underneath automobile with tool in hand,
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Follow Up By: Member - Roachie (SA) - Tuesday, Apr 12, 2005 at 22:39

Tuesday, Apr 12, 2005 at 22:39
I am absolutely speechless.....Bloody hell, the combined knowledge of you blokes astounds me.

Thank you all very much for such enlightenment....I hope we eventually meet up so I can buy ya's all a coldie!!!!

Ed, I have noticed that there is another one of those rubber condoms (sized so as to fit a midget haha) at the back on the heater hose, but always assumed that one was an outlet and the other was a return for some other piece of apparatas (spell???); but your assertion makes perfect sense and I will bleed the air out next time I change my coolant. Thanks.....
Roachie
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Reply By: Michael ( Moss Vale NSW) - Tuesday, Apr 12, 2005 at 21:14

Tuesday, Apr 12, 2005 at 21:14
To actually answer your question about BSP sizes, 1/8bsp is about 10mm on the thread, 1/4bsp is about 12mm and 3/8bsp is about 17mm on the dia of the thread. The fittings from the thermostat housing where the heater hoses go onto are 3/8 bsp. hope this helps as a guide. (GU 4.2) Michael
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Follow Up By: Member - Roachie (SA) - Tuesday, Apr 12, 2005 at 22:41

Tuesday, Apr 12, 2005 at 22:41
Thanks for that Michael.....

BTW have you had any over heating issues with your 2 beasts?

Cheers

Roachie
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Reply By: Member - Hugh (WA) - Tuesday, Apr 12, 2005 at 23:18

Tuesday, Apr 12, 2005 at 23:18
Hi Roachie,

Metric threads are classed by diameter (mm) and thread pitch (mm). The pitch increases with increasing diameter eg M5(0.8), M6(1.0), M8(1.25), M10(1.5), etc. You can buy thread gauges if your keen (for Metric, UNC, UNF, etc) or you can grab the verniers and work it out.

Next time you're in Adelaide call in to FJ Sweetman & Co and see if you can get a copy of their Industrial Fastener Reference Manual. This is an excellent reference. If you have specific thread query let me know as I have a copy.

Regards,
Hugh
AnswerID: 106461

Follow Up By: Jim-Bob - Wednesday, Apr 13, 2005 at 08:17

Wednesday, Apr 13, 2005 at 08:17
G'day Hugh.

The metric pitches you have quoted are for I.S.O. course threads, there is also I.S.O. fine, which as it's name implies is a finer pitch thread.

Safe travells
Jim-Bob.
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Reply By: muzzgit (WA) - Wednesday, Apr 13, 2005 at 01:33

Wednesday, Apr 13, 2005 at 01:33
Roachie, is there any reason why you aren't going to put the sender unit for the temp guage in the block ?

Most jap motors have a cooling system drain near the rear of the block. This is where I have fitted several temp guages in the past on several different engines. (not a diesel nissan though)

Food for thought.

cheers,

Muzz
AnswerID: 106469

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