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know your threads?
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Ray White



Joined: 02 Dec 2014
Posts: 4214
Location: Derby

PostPosted: Mon Sep 23, 2019 7:01 pm    Post subject: know your threads? Reply with quote

I found this quite interesting.

Full Nuts.

Nuts are almost always used opposite a mating bolt to fasten a stack of parts together. The two partners are kept together by a combination of their threads' friction, a slight stretch of the bolt, and compression of the parts.

Nuts are most commonly hexagonal in shape. It is important to use the correct sized spanners to avoid, ‘rounding off,’ the nut. Otherwise, if using an adjustable spanner you must ensure it is full tightened over the flat faces. Other specialized shapes exist for certain needs, such as wingnuts for finger adjustment and captive nuts (eg cage nuts) for hard to reach areas.



UNITS OF MEASUREMENT FOR THREAD TYPES

Metric Coarse and Metric Fine are in Millimetre (mm) units and were developed to simplify the imperial systems. Europe moved to this system but the Americans choose Imperial as their default. A coarse thread has less helical coils per mm and a fine one has more. Coarse is used for heavier loads and fine is used for lighter loads prone to vibrations.

British Association (BA) screw threads, named after the British Association for Advancement of Science, were devised in 1884 and standardised in 1903. Screws were described as "2BA", "4BA" etc., BA threads are specified by British Standard BS 93:1951 "Specification for British Association (B.A.) screw threads with tolerances for sizes 0 B.A. to 16 B.A." They are associated with metric units of measurement.

British Standards Brass (BSB) is a specialist thread form based upon the Whitworth thread and consisting of 26 threads per inch (imperial) whatever the thread diameter.

British Standard Cycle Thread (BSC) thread has extra fine threads 26 TPI originally for use on bicycles and motorcycles. The thread runs at a 60 degree rather than a 55 degree angle.

British Standard Threads are very rare and hard to source, hence, some of them are very expensive to replenish stocks.

British Standard Fine (BSF) thread form is based upon the British Standard Whitworth form but with a finer thread (more threads per inch) and has the same thread angle as the BSW and smaller thread depth.

British Standard Whitworth (BSW) is a thread form developed by Sir Joseph Whitworth in 1841. The thread form has rounded roots and crests, a thread angle of 55 degrees, the thread form is specified in BS 84: 1956



UNIFIED THREAD STANDARDS

The basic American standards for fastening screw threads as agreed upon by standard bodies of Canada, the United Kingdom, and the United States. They are a complete and integrated system of threads for fastening purposes. Their outstanding characteristic is general interchangeability of threads achieved through the standardization of thread form, diameter-pitch combinations, and limits of size



Unified National Coarse (UNC) is a thread form with a 60 degree flank angle rounded roots and flat crests. For a given diameter it has a larger thread pitch than an equivalent diameter UNF thread. The unified thread is based on inch sizes and was first standardised in 1948 unifying the Whitworth and American standard thread forms

Unified National Extra Fine (UNEF) is a Unified thread form with a very fine (small) pitch and are typically used on instruments and parts requiring a fine adjustment.

Unified National Fine (UNF) is a thread form with a 60 degree flank angle, rounded roots and flat crests. For a given diameter it has a smaller thread pitch than an equivalent diameter UNC thread.

Unified National (UN) thread form with a rounded root contour, applies only to external threads. (The UN thread form has a flat, or optionally, a rounded root contour.) The majority of fasteners with a Unified thread form (UNC UNF) have a rounded root contour.
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ukdave2002



Joined: 23 Nov 2007
Posts: 3666
Location: South Cheshire

PostPosted: Mon Sep 23, 2019 7:42 pm    Post subject: Reply with quote

Interesting.....I'm a bit of a thread geek Rolling Eyes...note to self "get a life"

I wonder if anyone can answer all 3 questions:

1) Whats the thread that Morris used on its 8's & 10's track rod ends? (hint its non of the threads in Rays post)

2) What thread do Smiths & Meccano share, and where do Smiths use it?

3) Which vehicle manufacturer mixes imperial & metric on the same screws & bolts?


Dave
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alanb



Joined: 10 Sep 2012
Posts: 514
Location: Berkshire.

PostPosted: Mon Sep 23, 2019 8:54 pm    Post subject: Reply with quote

I maybe wrong but I think
A) BSP
B) BA
C) Morris
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Ray White



Joined: 02 Dec 2014
Posts: 4214
Location: Derby

PostPosted: Mon Sep 23, 2019 8:55 pm    Post subject: Reply with quote

ukdave2002 wrote:
Interesting.....I'm a bit of a thread geek Rolling Eyes...note to self "get a life"

I wonder if anyone can answer all 3 questions:

1) Whats the thread that Morris used on its 8's & 10's track rod ends? (hint its non of the threads in Rays post)

2) What thread do Smiths & Meccano share, and where do Smiths use it?

3) Which vehicle manufacturer mixes imperial & metric on the same screws & bolts?


Dave


Morris/MG etc. used "mad metrics" in their engines and gearboxes. This was as a result of the Hotchkiss takeover during WW1. It's a fascinating tale.

This obsolete French Metric thread is a fine 8mm with a 1.00 mm pitch. It was used in place of 5/16" BSF. To make life easier for English mechanics the bolts had heads comparable with BSF size spanners.
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Rick
Site Admin


Joined: 27 Apr 2005
Posts: 21782
Location: UK

PostPosted: Mon Sep 23, 2019 9:56 pm    Post subject: Reply with quote

I have to confess that threads, and how to identify them, has always been something of a black art to me, saying that I've not studied them to the depth that some of you have. Was it UKDave that posted something here a few years ago on the subject?

RJ
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Various 1920s-1960s - Austin, Morris, Commer, Dodge etc.
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Ray White



Joined: 02 Dec 2014
Posts: 4214
Location: Derby

PostPosted: Mon Sep 23, 2019 11:24 pm    Post subject: Reply with quote

When my Dad passed away the accumulated stock of (mainly used) nuts and bolts in his garage presented me with something of a problem. What to do with thousands of fasteners most of which were filthy with oil and grease and in no order whatsoever.

In the end I collected them all together and soaked them in a bath of petrol. (Have you ever wondered what to do with old petrol?)

I then spent many an hour over several weeks pairing nuts with bolts; lubricating and sorting into boxes.
I now have a useful stock of nuts and bolts in different sizes of BSF, Whitworth, UNF, UNC, BA, Iso Metric coarse and fine together with some BSC and unknown threads that date back to the pre War era.

Dad was a Morris/MG man so I was surprised to find very few mad metric 8 x 1.00mm metric threads.

Plumbing and compressor fittings are in BSP and that is a whole other can of worms.

Austin, like Morris, was not averse to using the odd thread. I believe they used the unusual "Admiralty" thread for A 7 hub nuts.
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Kenham



Joined: 12 Mar 2012
Posts: 195
Location: Kent

PostPosted: Tue Sep 24, 2019 9:08 am    Post subject: Reply with quote

I am always surprised that more people do not get themselves a thread gauge a Vernier and a Zeus book, These will be most helpful in deciding just what bolt / screw / nut you need. A lot of people seem to think that every thread you come across must have a name , ie Whitworth, UNF etc, not always the case as all threads are just dia and threads per inch. Actual thread form will tell the difference between Whit and UNC etc etc although can still be the same Tpi. I have some very old taps and dies that are very strange sizes , unheard of if you want to put a name to them. probably made by some steam engine builder.
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consul 57



Joined: 09 Nov 2017
Posts: 316
Location: somerset

PostPosted: Tue Sep 24, 2019 10:11 am    Post subject: Reply with quote

thank god for metric, so much easier!
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Ray White



Joined: 02 Dec 2014
Posts: 4214
Location: Derby

PostPosted: Tue Sep 24, 2019 10:23 am    Post subject: Reply with quote

Kenham wrote:
I am always surprised that more people do not get themselves a thread gauge a Vernier and a Zeus book, These will be most helpful in deciding just what bolt / screw / nut you need. A lot of people seem to think that every thread you come across must have a name , ie Whitworth, UNF etc, not always the case as all threads are just dia and threads per inch. Actual thread form will tell the difference between Whit and UNC etc etc although can still be the same Tpi. I have some very old taps and dies that are very strange sizes , unheard of if you want to put a name to them. probably made by some steam engine builder.


Knowing what a fixing it is should dictate which spanner to use. Nothing pi^^es me off more than rounded corners on a hex nut.!
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alastairq



Joined: 14 Oct 2016
Posts: 1541
Location: East Yorkshire

PostPosted: Tue Sep 24, 2019 1:42 pm    Post subject: Reply with quote

Ray White wrote:


Knowing what a fixing it is should dictate which spanner to use. Nothing pi^^es me off more than rounded corners on a hex nut.!


Even then, a spanner may not be as tight a fit as the 'size' would suggest? Sad
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Ray White



Joined: 02 Dec 2014
Posts: 4214
Location: Derby

PostPosted: Tue Sep 24, 2019 3:09 pm    Post subject: Reply with quote

alastairq wrote:
Ray White wrote:


Knowing what a fixing it is should dictate which spanner to use. Nothing pi^^es me off more than rounded corners on a hex nut.!


Even then, a spanner may not be as tight a fit as the 'size' would suggest? Sad


Perhaps all spanners of the same size are made equal but maybe some are more equal than others. Wink
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alastairq



Joined: 14 Oct 2016
Posts: 1541
Location: East Yorkshire

PostPosted: Tue Sep 24, 2019 3:44 pm    Post subject: Reply with quote

Indeed!

I have a nice shiny spanner...supposedly 5/8ths AF....not in the least bit doubtful looking..yet,,the jaws are something else! Fine on the side pointing to the right....but slack if pointing the other way round.
In other words, within the thickness of the jaws, one side fits, the other doesn't..they're 'bevelled'.....
I didn't buy it....came in a toolkit belonging to an even more ancient relative.

However, I call it my ''Joy & Consternation'' spanner....deep joy one way round, huge disappointment the other!
Took a while for me to work out what was going wrong with the thing.
_________________
Dellow Mk2, 1951 built, reg 1952.
Ford Mustang coupe, 1967, 6 cylinder auto.
Fiat 126 BIS
Cannon special [1996 registered. Built in 1950's]
----------------------------------------------
Ford Pop chassis, Ashley 1172 bodyshell, in pieces.
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Ray White



Joined: 02 Dec 2014
Posts: 4214
Location: Derby

PostPosted: Tue Sep 24, 2019 4:53 pm    Post subject: Reply with quote

How about these? Ideal for the lazy "that'l do" approach. Razz

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Phil - Nottingham



Joined: 01 Jan 2008
Posts: 1252
Location: Nottingham

PostPosted: Tue Sep 24, 2019 9:58 pm    Post subject: Reply with quote

Metrinch are useful sometimes for rounded off flats - if not rounded they will be in after using them
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Ray White



Joined: 02 Dec 2014
Posts: 4214
Location: Derby

PostPosted: Tue Sep 24, 2019 10:12 pm    Post subject: Reply with quote

Phil - Nottingham wrote:
Metrinch are useful sometimes for rounded off flats - if not rounded they will be in after using them


I think you mean rounded off corners. Wink
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