Threads

[Ramblingman]

According to an American supplier a thread was described as ½”-20 but it turned out to be ½” UNF with 20 being the teeth per inch which I am told is a completely different thread altogether.

This happened again with the following
3/8”-24
5/16”-18
¼”-20

So does this mean that they are actually as follows and if so why don’t they just say that?!

3/8” UNF

5/16” UNC
¼” UNC

Also I have a thread gauge which is stamped as 55 degrees whitworth and 60 degrees metrisch. The blades are 0.25 up to 6.0 and the other set are 62G up to 4G.
So which would I use to measure the above discussed threads (metric and SAE are 60 degree I believe but the range seems too small) and what are the “G” blades?

All help appreciated as I am getting more confused the more I try to understand it all :confused:

[weemark]

UNF and UNC threads will be set by a standard - just because another bolt has the same amount of threads per inch doesnt mean the pitch of the threads meets the UNF/UNC standards hence the reason they are not advertised the as such.

if you have a look at this chart it shows loads of bolt sizes and all their other dimensions http://www.watchman.dsl.pipex.com/thread.html - if you go down to 1/2" you can see there are three different types of bolt with 20tpi.

UNF and UNC both have a thread angle of 60 deg.

[MisteR Tee]

My wheel nut threads (imperial anyway) are 1/2" x 20 unf, so are the 3/8", 7/16" & 5/8" but I don't know about the other sizes you mentioned.

[Knowledge]

Unified (UNF UNC) is an American standard thread pitch. I always have a Zues book around to give myself the common thread sizes. 55 Deg is as said Whitworth which is an English standard. UNF/UNC Unified (And most others) are 60 Deg. I guess your guages are German or Swiss as it says 60 Deg 'Metric'. That 0.25 is 0.25 mm thread pitch.
With Whit and UNF/UNC It IS possible to sometimes get a nut and bolt from each that will screw together, but a 55 Deg bolt in a 60Deg nut is a no no... If unsure as a rule check the head size of the bolt, Whitworth bolts and nuts have a specific AF compared to UNF/UNC, but you'll need a chart to find the sizes.

Saying 1/2" 20 to me IS 1/2" UNF... It's just a matter of choice how you note it.

Now if you REALLY want to get complicated start talking thread fits!!! 6g refers to a G fit. Guages come in different forms, some are like flat topped screws others a type of parrallel pair of teath that you measure across, but a 6G 'Go' should screw on or in to a good thread, and the No-go NOT. Theres a range of fits depending on how you want your thread to be. Others are H or h. The cap or lower case refers to the fit being either internal or external fit. Again there's a chart for fits with letters and numbers for each 'fit' range.

[stueeee]

As said, UNC/UNF threds are 60 degree. Whitworth (and BSF) threads are 55 degree.

The TPI (Threads per Inch) count of a lot of UNC sizes -1/4" 5/16" etc. are the same for whitworth and UNC. Mixing these is real bad news because the nut and bolt threads will only make contact at the root and crest of the thread resulting in very poor retaining strength.

It's very difficult to see the difference between a 60 degree and 55 degree thread with the naked eye and a thread gauge.

Whitworth nuts and bolts are easily spotted though, because of their peculiar AF (across flats) sizes which are .445" for 1/4", .525" for 5/16" and .600" for 3/8" as against 7/16", 1/2" an 9/16" for the UNC sizes. Basically if your AF spanner isn't a good fit on a nut or bolt there's a good reason for that; change the nut or bolt for the correct one.

Stuart.

[Ramblingman]

Thanks all for the explanations – very much appreciated – but I apologise that I am still finding this hard going :o
I don’t expect to be an expert overnight but what I would like to be able to do is identify a thread in a component myself and understand what a thread is when the component comes with such information. (I say component as it is not nuts and bolts that I am so interested in at the moment but senders and remote oil filter heads etc.)

So my oil temperature gauge sender literature says ½”-20
A fittings supplier told me that it is an uncommon thread – no mention of it being UNF
My local engineer tells me it is not ½”-20 (that’s a different thread he says) but is ½”UNF
Mark says it could be 1 of 3 threads with that diameter and tpi
Knowledge says 1/2"- 20 is another way of saying 1/2" UNF
So you see my confusion – how would I / should I have known what the thread was??

So are these assumptions on my part correct (having looked in my Zeus book)
3/8”-24 = 3/8” UNF
5/16”-18 = 5/16” UNC
¼”-20 = ¼” UNC

So what is the best gauge to get that would enable me to measure the above tpi figures as mine does not seem to be what I need?

“It's very difficult to see the difference between a 60 degree and 55 degree thread with the naked eye and a thread gauge” - glad you said that Stuart so I won’t even get into that:)

[langysrodshop]

I take it you don't read Custom Car Ceri :D



Thanks all for the explanations – very much appreciated – but I apologise that I am still finding this hard going :o
I don’t expect to be an expert overnight but what I would like to be able to do is identify a thread in a component myself and understand what a thread is when the component comes with such information. (I say component as it is not nuts and bolts that I am so interested in at the moment but senders and remote oil filter heads etc.)

So my oil temperature gauge sender literature says ½”-20
A fittings supplier told me that it is an uncommon thread – no mention of it being UNF
My local engineer tells me it is not ½”-20 (that’s a different thread he says) but is ½”UNF
Mark says it could be 1 of 3 threads with that diameter and tpi
Knowledge says 1/2"- 20 is another way of saying 1/2" UNF
So you see my confusion – how would I / should I have known what the thread was??

So are these assumptions on my part correct (having looked in my Zeus book)
3/8”-24 = 3/8” UNF
5/16”-18 = 5/16” UNC
¼”-20 = ¼” UNC

So what is the best gauge to get that would enable me to measure the above tpi figures as mine does not seem to be what I need?

“It's very difficult to see the difference between a 60 degree and 55 degree thread with the naked eye and a thread gauge” - glad you said that Stuart so I won’t even get into that:)

[weemark]

ceri most parts on older usa cars have UNC or UNF threads, ignore the rest :)

[Adam]

Every thread on a sbc or BBC is UNC apart from the main balancer bolt who's size I forget and bottom pulley bolts which are 3/8 UNF.

[Knowledge]

Thanks Stuee.. I forgot BSF is also 55 Deg.
If your filter housing says 1/2" 20 and is for an American engine I see no reason to doubt it's UNF. The guy who says it's an unusual thread is wrong as 1/2" UNF is a very common thread. I wouldn't worry about Whit and BSF if it's american as they just won't be using that size. The ONLY time you really see GB threads outside of our shores is on pipe fittings and that BSP. Even then most American brake pipe fittings are still UNF. If you can lay your hands on a 1/2" UNF wheel bolt just try that in your filter housing and you'll soon know if it's right.

EDIT:
Just thought. Maybe he's saying a 1/2" UNF is unusual for the filter housing? I'm not sure where you're getting the 1/2" 20 fact from, but if you want to check the thread pitch here's a tip. Get a pencil and a piece of paper. Wrap the paper tight around the pencil. Put it inside the hole and carefully run it around the thread for a moment applying pressure. Take it out and using a ruler count how many lines you have over an inch or half inch... Not a perfect method I admit, but it's usually a good guide to size.

[langysrodshop]

Like all other V8's



Every thread on a sbc or BBC is UNC apart from the main balancer bolt who's size I forget and bottom pulley bolts which are 3/8 UNF.

[Ramblingman]

Thanks for all the further replies.
Mark – I like that idea of assume UNC or UNF and ignore the rest – I think that suits my skill level:o The only problem with that theory of course is that not all “american” products are actually made there but more like in China……………:)
Knowledge – the ½” UNF thread in question is for an oil temperature gauge sender and the information came from the maker. Perhaps the comment re uncommon thread related to such senders not usually being that thread as this seems to be the case from the fittings I have found to take such senders.
Steve – of course I read CC (doesn’t everyone:eek:) and that article of yours wasn’t bad (but a bit basic for my me of course:rolleyes:) but you really should have let me proof read it for you so I could have told you what bits I wanted you to cover…………part 2 gone to the printers yet…………may not be too late……….;)
Adam – I am sure you are trying to send me subliminal messages of “get a chevy, get a chevy” - it probably would be a lot easier:bang:.
So as my pitch gauge does not seem to be what I need what sort of gauge should I be looking for that will cover the tpi figures for UNC and UNF as well as NPT and maybe BSP?
Also why does BSP not feature in my Zeus book I wonder?

[MisteR Tee]

... The only problem with that theory of course is that not all “american” products are actually made there but more like in China……………:)[/SIZE][/FONT]



But are made to US spec, as all wheel nuts are sourced from there!!;)

[weemark]

Thanks for all the further replies.
Mark – I like that idea of assume UNC or UNF and ignore the rest – I think that suits my skill level:o The only problem with that theory of course is that not all “american” products are actually made there but more like in China……………:)


it doesnt matter where its made... its what its going on that matters. the only threads you need to worry about are UNF, UNC and NPT, early yank tin didnt use anything else.

[stueeee]

So as my pitch gauge does not seem to be what I need what sort of gauge should I be looking for that will cover the tpi figures for UNC and UNF as well as NPT and maybe BSP?
Also why does BSP not feature in my Zeus book I wonder?

BSP should appear as British Standard Pipe thread in your Zeus book if it's like mine.

You need different thread gauges for UNF/UNC/NPT (which are all 60 degree angle threads) these gauges will also include the odd pitches used for american threads e.g. 13 TPI for 1/2" UNC

BSF/BSW/BSP are all 55 degree threads, so you should be using 55 degree "Whitworth" style gauges for all these.

With the larger threads, you can see the difference if you use a 55 degree gauge on a 60 degree thread (or vice versa) even if the thread count is right.

This is the kind of thing you need to cover pretty well everything you'll come across: http://cgi.ebay.co.uk/RDG-SET-SCREW-PITCH-THREAD-GAUGES-BSW-METRIC-UNF-UNC-/370494502112?pt=UK_Home_Garden_PowerTools_SM&hash=item56433174e0

Stuart.

[Knowledge]

BSP should appear as British Standard Pipe thread in your Zeus book if it's like mine.

Stuart.

Sadly the latest Zues ooks come without BSP thread. If you need any info on them just ask as I have a book of just about every thread in existance. Bicycle thread, bottle top thread, Swiss horolagy (OK clocks to you).

I don't think you NEED thread guages. These are used to check FIT. I used to use them to check machined size during manufacture. Just find a UNF or UNC bolt and try it in. Just make sure everythings clean and free of burrs and if it doesnt screw in easily it isn't that thread.

[stueeee]

if it doesnt screw in easily it isn't that thread.

Or, the thread you're trying to screw into is damaged, otherwise that approach is fine if it's UNF or UNC, which is most fasteners are; how's your stock of UNEF/UNS/ANF/NPS nuts and bolts for checking out the other threads?

I've found plenty of these threads (and some others) working on US manufactured cars and trucks. The quickest (often the only) way to be sure of what thread you have, is to measure its diameter with vernier calipers or a mic. and then check the thread pitch with a gauge.

[Knowledge]

I've found plenty of these threads (and some others) working on US manufactured cars and trucks. The quickest (often the only) way to be sure of what thread you have, is to measure its diameter with vernier calipers or a mic. and then check the thread pitch with a gauge.

For others who read this benifit. Thread guages come in the following types:-
Fit guage. Looks like two screws either end of a handle. One is bigger than the other. Go 'should' screw in. No-go 'shouldn't.
Pitch guage. Looks like a flat piece of sheet steel (Cos it is) has an edge with teeth on it. You try them against the thread, if it matches THAT is your thread pitch. These are fairly cheap too. Get a Metric, Unified, and British standard 55 deg set and you're away.

They call me knowledge for good reasons :-)

[Ramblingman]

Thanks all for the further info. – sorry for the delay in responding but I had to have a lay down in a dark room to recover from all this technical info. :D
Mark / Maurice – I see what you mean but in my mind I was thinking not so much about specific car parts but for example a finned radiator cap cover I bought that had a missing grub screw and I just assumed being yank it would not be metric when in fact it was.

Knowledge / Stuart – sorry I made a mistake, my Zeus book does include BSP – what I meant to say was that it does not list NPT (which I would like as it seems a popular thread for senders etc.) -- does yours? I seem to have the rest of the main ones mentioned except BSW (and UNEF/UNS/NPS whatever they are….).

I have a remote head for an oil filter and the ports measure ¾” diameter and have 14tpi – I am told this is probably ½” NPT but that 7/8” UNC has those same specs and both threads are 60 degrees ……..so how would you know which it is:confused:

For the inexperienced like me trying a bolt is probably the answer for most situations but for that I will have to up my stock of non metric stuff.:eek:

I have a digital vernier calliper so just need the gauges now (I have the one described in my original post so that should cover the metric?) but can’t quite see what I need (not sure if the ebay one covered the rest?). I am guessing that you have had yours man and boy as it were but do you know of a good supplier I could try or are any of these any good?


http://www.toolfastdirect.co.uk/acatalog/Moore_and_Wright_Screw_Pitch_Guages_.html (http://www.toolfastdirect.co.uk/acatalog/Moore_and_Wright_Screw_Pitch_Guages_.html)

http://www.axminster.co.uk/axminster-metric-imperial-thread-pitch-gauge-prod23483/ (http://www.axminster.co.uk/axminster-metric-imperial-thread-pitch-gauge-prod23483/)

http://www.chronos.ltd.uk/acatalog/Screw-Pitch-Gauges.html (http://www.chronos.ltd.uk/acatalog/Screw-Pitch-Gauges.html)


Is this also worth having too?

http://www.chronos.ltd.uk/acatalog/Screwcutting-Gauge.html (http://www.chronos.ltd.uk/acatalog/Screwcutting-Gauge.html)

[langysrodshop]

Easy to tell the difference in NPT & UNC, NPT is a taper thread, UNC isn't.




Thanks all for the further info. – sorry for the delay in responding but I had to have a lay down in a dark room to recover from all this technical info. :D
Mark / Maurice – I see what you mean but in my mind I was thinking not so much about specific car parts but for example a finned radiator cap cover I bought that had a missing grub screw and I just assumed being yank it would not be metric when in fact it was.

Knowledge / Stuart – sorry I made a mistake, my Zeus book does include BSP – what I meant to say was that it does not list NPT (which I would like as it seems a popular thread for senders etc.) -- does yours? I seem to have the rest of the main ones mentioned except BSW (and UNEF/UNS/NPS whatever they are….).

I have a remote head for an oil filter and the ports measure ¾” diameter and have 14tpi – I am told this is probably ½” NPT but that 7/8” UNC has those same specs and both threads are 60 degrees ……..so how would you know which it is:confused:

For the inexperienced like me trying a bolt is probably the answer for most situations but for that I will have to up my stock of non metric stuff.:eek:

I have a digital vernier calliper so just need the gauges now (I have the one described in my original post so that should cover the metric?) but can’t quite see what I need (not sure if the ebay one covered the rest?). I am guessing that you have had yours man and boy as it were but do you know of a good supplier I could try or are any of these any good?


http://www.toolfastdirect.co.uk/acatalog/Moore_and_Wright_Screw_Pitch_Guages_.html (http://www.toolfastdirect.co.uk/acatalog/Moore_and_Wright_Screw_Pitch_Guages_.html)

http://www.axminster.co.uk/axminster-metric-imperial-thread-pitch-gauge-prod23483/ (http://www.axminster.co.uk/axminster-metric-imperial-thread-pitch-gauge-prod23483/)

http://www.chronos.ltd.uk/acatalog/Screw-Pitch-Gauges.html (http://www.chronos.ltd.uk/acatalog/Screw-Pitch-Gauges.html)


Is this also worth having too?

http://www.chronos.ltd.uk/acatalog/Screwcutting-Gauge.html (http://www.chronos.ltd.uk/acatalog/Screwcutting-Gauge.html)

[weemark]

ceri i find it amazing how much focus you are putting into finding out about a bolt then moving onto equipment for measuring them - not a criticism, just an observation, makes my mind boggle.

[langysrodshop]

Ceri is very exacting :D



ceri i cant believe how much focus you are putting into finding out about a bolt then moving onto equipment for measuring them - not a criticism, just an observation.

[stueeee]

Never seen NPT chart in any of my Zeus books old or new; A book called "A Guide to world screw threads" authored/edited by P A Sidders has the specs. of every thread imaginable, but is probably too much information -and it doesn't fit in your overall pocket like a Zeus book either. NPT dimensions are here on the web: http://www.engineeringtoolbox.com/npt-national-pipe-taper-threads-d_750.html

Any hole or boss which carries fluid on an american car or truck will be NPT if it's tapered orr NPS (National pipe Straight) if it's a parallel thread like the connections used on oil pressure gauges etc.

Only had quick look, but the Moore and Wright pitch gauges you linked to look OK. The screwcutting gauge in your last link is really useful if you are going to do screwcutting on a lathe, and it's essential if you also grind your own cutting tools. Otherwise, you probably won't use one.

FYI, UNEF = Unified National Extra Fine, UNS = Unified National Special, ANF=American National Fine (Also Known As Sellers thread)

HTH, Stuart.

[Ramblingman]

Mark
I can see how you may be viewing this and I am not taking offence or anything but perhaps I should just clarify. I come on here to learn as I have no technical or trade background and I do not exactly live in a hot bed of hot rod activity. Partly due to my naturally curious nature it does not satisfy me to know the answer to a particular question but I need to understand why and hopefully not to have to ask the same question again i.e. I could just ask “what is this thread on this engine” but far better I learn how to measure threads for myself. Plus it’s cheaper than evening classes:) This of course is bad news for all the kind people like yourself who take the time to reply. Just remember the devil is in the detail.:D

Steve
I have been called worse than exacting:rolleyes:.
Regarding the taper thread I see what you mean – I take it this is easy to see the difference? – funny my local engineer did not apply that logic as it was he who was unable to tell me which it was and suggested I got both bolt types and try them for fit.
Off now to read CC and that great article on nuts – don’t be surprised if it does not prompt a question. LOL

Stuart
Thanks for the further info. and the NPT link – much appreciated.

My oil pressure gauge is electrical and the sender thread is supposed to be 1/8” NPT. I assume you mean the NPS thread would be on a mechanical gauge as it is actually carrying oil – am I right here?

Regarding the gauges thanks for looking at the links. I have since found this in machine mart which covers 4-42 TPI which would cover most of my needs (and should keep me on the vat free invite list for a minimal outlay;)).

http://www.machinemart.co.uk/shop/product/details/et158-screw-pitch-gauge-usa-60 (http://www.machinemart.co.uk/shop/product/details/et158-screw-pitch-gauge-usa-60)

[stueeee]

I assume you mean the NPS thread would be on a mechanical gauge as it is actually carrying oil – am I right here?



Yes,
Gauges have parallel threads. Yank gauges will usually have a 1/16" or 1/8" NPS threaded boss.

Stuart.

[langysrodshop]

Ceri if your friend the engineer didn't know that he's not very good i would say !!!



Mark
I can see how you may be viewing this and I am not taking offence or anything but perhaps I should just clarify. I come on here to learn as I have no technical or trade background and I do not exactly live in a hot bed of hot rod activity. Partly due to my naturally curious nature it does not satisfy me to know the answer to a particular question but I need to understand why and hopefully not to have to ask the same question again i.e. I could just ask “what is this thread on this engine” but far better I learn how to measure threads for myself. Plus it’s cheaper than evening classes:) This of course is bad news for all the kind people like yourself who take the time to reply. Just remember the devil is in the detail.:D

Steve
I have been called worse than exacting:rolleyes:.
Regarding the taper thread I see what you mean – I take it this is easy to see the difference? – funny my local engineer did not apply that logic as it was he who was unable to tell me which it was and suggested I got both bolt types and try them for fit.
Off now to read CC and that great article on nuts – don’t be surprised if it does not prompt a question. LOL

Stuart
Thanks for the further info. and the NPT link – much appreciated.

My oil pressure gauge is electrical and the sender thread is supposed to be 1/8” NPT. I assume you mean the NPS thread would be on a mechanical gauge as it is actually carrying oil – am I right here?

Regarding the gauges thanks for looking at the links. I have since found this in machine mart which covers 4-42 TPI which would cover most of my needs (and should keep me on the vat free invite list for a minimal outlay;)).

http://www.machinemart.co.uk/shop/product/details/et158-screw-pitch-gauge-usa-60 (http://www.machinemart.co.uk/shop/product/details/et158-screw-pitch-gauge-usa-60)

[Knowledge]

Just the one point to be made here as all else is covered. Zues book is a UK/European publication and a very small book. It's a very useful book I recommend to everyone. But it only carries the most common info and as NPT and NPS are specifically used in America (Even the Europeans and Japanese tend to use BSP and BSPT) obviously Zues didn't put that in. Incidentally be careful using the thread gauges in a taper thread as obviously they don't exactly fit because of the thread being tapered. Actually most of NPT is the same as BSPT, But you get a few changes like 1/4 NPS has 18tpi and 1/4 BSP is 19tpi. I'll sign off with a tip. If you're trying to clean out a taper thread (WITH a taper tap I trust) give it JUST a 1/4 to a 1/2 turn and NO MORE. A taper thread gets oversized very quickly.

[Ramblingman]

Stuart -- Thanks for clarifying regarding the gauges as you had me worried there for a minute that my sender was not the thread I thought it was:eek:
Steve – I guessed that may be your reply:) – anyway I didn’t mean to pull others into this but all I can say is around here he is the best we have with a very good reputation and it is a third generation business (he still being old enough to be trained in the old ways) so perhaps he was having a bad day or I had just worn him down:o
One last question – yeah I know, sorry……….according to the link on NPT threads they require sealing but NPTF do not. Is this correct as according to the gauge sender installation instructions it stresses NOT to use any form of sealant on the 1/8” NPT threads?