UNC or UNF thread ?

[Rhys]

Hi all, I’m looking to buy some imperial nuts and bolts for workshop supplies, I have a 1974 MK2A Commando and a 1974 MGB GT not sure if I need UNC or UNF thread ? Or something else ? Thanks in advance for your help, Rhys.

 

[Stephen Hill]

https://www.accessnorton.com/NortonCommando/british-standard.21413/#post-319659

 

[Rhys]

https://www.accessnorton.com/NortonCommando/british-standard.21413/#post-319659

That thread appears to be about tool types and sizes not thread sort or fixing size ?

 

[Mr. Rick]

Not sure what the reference to "imperial" means, but I'm pretty sure that UNF and UNC are only different w respect to the number of threads per inch.
So you'd have for example UNF 7/16 being 20 TPI and 7/16 UNC at 14 TPI.
Just generally speaking, and this is not always true, the engine and gearbox fasteners are Whitworth (neither UNF or UNC).
I found somewhere on the bike (sorry, can't remember where) that even a metric wrench was a better fit than either of the others.
In short, it's all over the map, and I've given up buying in advance.
Here's an idea of what you might run into: https://www.nortonownersclub.org/support/technical-support-general/screw-threads
And here's a place you might use if you have the part number: http://stainlessbits.com/link12a.html

 

[ashman]

UNF is find thread and UNC is a courser thread or BSF or BSW is what is normaly used on British cars and motorcycles of old but Norton also use bicyles threads as well different size threads per inch, I was lucky I worked in a maintenance workshop that had every tap and die sets for any job and when they closed the workshop down I slowly aquired all the imperal taps and dies but didn't grab the metric sets, I built up a good workshop full of tools at the time and has worked out good for me now having a lathe and milling machine and having taped drills up to 25mm.
For home use there are plenty of cheap tap and die sets around with everything you need for older British cars and motorcycles and swap meets are also a good place to look.

Ashley

 

[Fast Eddie]

If you have a ‘74 Norton and a ‘74 MG, then on those two vehicles you probably have every type of thread type known to man!

The Nort will have mainly UNF on the cycle parts I think, and a mainly BS in the engine I think.

The MG will have whatever was lying around the place at the time.

And both will have whatever 44 years of previous owners had lying around the place!

So... mixed UNF, BSF and BSW from 1/4 to 3/8 should get you along the way I think.

 

[850commando]

Hi all, I’m looking to buy some imperial nuts and bolts for workshop supplies, I have a 1974 MK2A Commando and a 1974 MGB GT not sure if I need UNC or UNF thread ? Or something else ? Thanks in advance for your help, Rhys.

I use the bolt supply house as my workshop supplies, they stock both UNC and UNF sizes in Gr5 and Gr8, there are way to many sizes and lengths involved when talking norton or mg, why lock up your money in a bin of nuts and bolts?

 

[Madnorton]

Pretty certain the MG by this time will have much the same range of threads as the Norton as they were both destined for a North American market.
On a Norton Commando, you will find BA, UNF, BSC, CEI - yes, the same but some of the original pre rationalised sizes still used, Whitworth, Whitworth form, UNC occasionally and Metric on the reflectors if you have them. Botched threads will usually be botched to BSF - usually found on the NOVA bikes from the US.

Spanners and sockets can be sourced from car boot sales, though prices have seemed to have gone up these days, Elora, King Dick and other quality spanners used to be had for 20p. Look for Whit, BS, AF sizes,

Wish I had a £ for everytime someone has complained about threads on a Norton.

 

[Fast Eddie]

why lock up your money in a bin of nuts and bolts?

Isn’t it obvious?

Because you need to have plenty of each size, stored in clearly marked bins, with the bins arranged in ascending size order, along with appropriate nuts and washers, also, obviously, clearly labelled.

And then your Unified combination spanner’s (wrenches) and BS spanner’s, and metric spanner’s, in pairs, on their clearly marked shadow boards.

Or is it just me...!?

 

[cliffa]

Or buy some Metrinch sockets / spanners. I've never used them, but I've heard good things.

 

[Peter R]

If you are serious about repair or maintenance of your Norton, or any other older british bike/car for that matter, invest in a good set of Withworth sockets and spanners while they are still available.
I hate to mess up fasteners with non fitting spanners, it's the telltale sign of a bodged up machine.

 

[gripper]

BSW and BSF have a thread form of 55 degrees and generally the spanner sizes are unique to the whitworth form though the Cycle threads use the the same spanner sizes but have a 60 degree form. UNF, UNC, Metric fine and coarse have a 60 degree form. UNF and UNC have a imperial spanner size across the flats and metric screws have across the flats metric spanners. Finally BA threads are 47 degrees and have a unique size and their own spanner sizes.
Brit cars from the sixties will have generally UNF and UNC threads until the eighties when the industry started to go metric. There was a morris minor made I believe with totally metric screws.

 

[oldbeezer]

BSW and BSF have a thread form of 55 degrees and generally the spanner sizes are unique to the whitworth form though the Cycle threads use the the same spanner sizes but have a 60 degree form. UNF, UNC, Metric fine and coarse have a 60 degree form. UNF and UNC have a imperial spanner size across the flats and metric screws have across the flats metric spanners. Finally BA threads are 47 degrees and have a unique size and their own spanner sizes.
Brit cars from the sixties will have generally UNF and UNC threads until the eighties when the industry started to go metric. There was a morris minor made I believe with totally metric screws.

Thanks!

 

[texasSlick]

If you are in the US, a good supplier of Brit tools and fasteners is:

https://britishfasteners.com

+1 on Peter R's post.

Slick

 

[Hobot]

Metrinch sockets / spanners I found may work where nothing else fits a buggered bolt head or nut and can't get Vice Grip pliers on them or a nut cracker or too tight quarters to risk torch cutting. Only issue with Metrinch is can't replace a single socket as only compete sets sold, ugh. Whitworth 1/4 - 3/8 bent wrench needed for main engine fasteners. 14mm socket fits head bolts well. 9/16" fits most the rest the best. Whitwhorth 55* threads is slightly stronger than 60* but both mate very well. Trickiest threads to find are Amal carb and ignition mount screws, which are same as holds Lake Injector air filter on Drouins. Dang ignition center bolt comes in two tread form flavors to keep in mind ordering. I bought one each as not equipped to decide but by trial error later.

 

[Stephen Hill]

Rhys wrote: "
https://www.accessnorton.com/NortonCommando/british-standard.21413/#post-319659
That thread appears to be about tool types and sizes not thread sort or fixing size ?"

If you read the thread, your original question "I need UNC or UNF thread ? Or something else ?" would be answered.

Such as (extracted from the thread):

Almost all the CYCLE PARTS on a Commando use american fasteners -= UNF. (used to be called NF or SAE)
So american wrenches are made for them and will fit perfectly.
The engine and gearbox are a different matter, they are mostly BS cycle thread,
and a bit of everything else thrown in, as mentioned above.
If you see the interlinked circles symbol on the nuts on a Commando, it means its UNF.

When the Commando was first built, the British motor industry was converting to the American Unified system. So the vast majority of cycle parts are UNF/UNC. The engine & gearbox on the other hand, were only supposed to be a stop gap fitment until a more modern engine could be prepared. As we all know, this never happened & hence the continued use of Imperial thread forms i.e BSW/BSF/BSc for engine & gearbox. Electrical items use BA thread forms.

The Commando had a considerable quantity of *Unified* threads from the beginning, and although some BS threads were later changed to Unified the actual number was relatively small, so there's not all that much difference between early and late model Commandos.

The “UN” thread form was developed after World War II by representatives of Great Britain, Canada, and the United States of America, to prevent recurrence of the wartime difficulties in supplying fasteners and tools in both British Standard Whitworth and US Standard configurations when and where needed. In 1949, after years of committee meetings between Canada, England and United States of America the American National Standard Series was replaced with the Unified Inch Standard Series. In the end there were three base reasons identified for the change. The first reason was to provide interchangeability with Canada and United Kingdom. The second reason was to allow for interchangeability in the growing global marketplace. The third reason was to correct certain thread production difficulties. The jointly-developed thread form was named the Unified Thread Form. the Unified Thread is also referred to in the B1.1-2003 as Unified Inch Screw Thread. This Unified Inch Screw Thread both superseded the previous British, Canadian and American national standards, and later served as a prototype multi-national thread form standard that was eventually metricified to become the ISO Metric Screw Thread (the M-series).

Mk3 switch gear (Veglia Lucas) fastens with 4mm and 5mm allen and panhead cap screws.


The thread size on the Amals, points cover and gearbox inspection cover are #2 BA.

 

[cliffa]

If you are serious about repair or maintenance of your Norton, or any other older british bike/car for that matter, invest in a good set of Withworth sockets and spanners while they are still available.
I hate to mess up fasteners with non fitting spanners, it's the telltale sign of a bodged up machine.

I totally agree Peter. I understand that the Metrinch are what as known as "Flank Drive" i.e. they bear on the flat of the hexagon and not on the tip, so there is no chance of rounding off the corners. In fact as Hobot said they have been known to remove almost completely rounded nuts and bolts I believe. They are pretty expensive, but come with a lifetime warranty. I have more than enough Metric and Imperial tools, but if I were starting out I'd certainly consider them.


cliffa

 

[Bodger]

I think Stephen Hill provides a comprehensive response to the original inquiry. Some of the never-ending confusion surrounding this subject may be caused by the American cousins insistence on calling all 'Imperial" fasteners (BSF, CEI, Whitworth, BA, etc.) "Whitworth." Since it was the "British" and not the "American" empire that developed and used these thread forms, it makes more sense to lump them all together as "Imperial" fasteners and call the "Unified" fasteners "Unified," although some people refer to them as SAE. So now my question is, when they make Buicks in China do they use metric fasteners?

 

[Rhys]

Rhys wrote: "
https://www.accessnorton.com/NortonCommando/british-standard.21413/#post-319659
That thread appears to be about tool types and sizes not thread sort or fixing size ?"

If you read the thread, your original question "I need UNC or UNF thread ? Or something else ?" would be answered.

Such as (extracted from the thread):

Almost all the CYCLE PARTS on a Commando use american fasteners -= UNF. (used to be called NF or SAE)
So american wrenches are made for them and will fit perfectly.
The engine and gearbox are a different matter, they are mostly BS cycle thread,
and a bit of everything else thrown in, as mentioned above.
If you see the interlinked circles symbol on the nuts on a Commando, it means its UNF.

When the Commando was first built, the British motor industry was converting to the American Unified system. So the vast majority of cycle parts are UNF/UNC. The engine & gearbox on the other hand, were only supposed to be a stop gap fitment until a more modern engine could be prepared. As we all know, this never happened & hence the continued use of Imperial thread forms i.e BSW/BSF/BSc for engine & gearbox. Electrical items use BA thread forms.

The Commando had a considerable quantity of *Unified* threads from the beginning, and although some BS threads were later changed to Unified the actual number was relatively small, so there's not all that much difference between early and late model Commandos.

The “UN” thread form was developed after World War II by representatives of Great Britain, Canada, and the United States of America, to prevent recurrence of the wartime difficulties in supplying fasteners and tools in both British Standard Whitworth and US Standard configurations when and where needed. In 1949, after years of committee meetings between Canada, England and United States of America the American National Standard Series was replaced with the Unified Inch Standard Series. In the end there were three base reasons identified for the change. The first reason was to provide interchangeability with Canada and United Kingdom. The second reason was to allow for interchangeability in the growing global marketplace. The third reason was to correct certain thread production difficulties. The jointly-developed thread form was named the Unified Thread Form. the Unified Thread is also referred to in the B1.1-2003 as Unified Inch Screw Thread. This Unified Inch Screw Thread both superseded the previous British, Canadian and American national standards, and later served as a prototype multi-national thread form standard that was eventually metricified to become the ISO Metric Screw Thread (the M-series).

Mk3 switch gear (Veglia Lucas) fastens with 4mm and 5mm allen and panhead cap screws.


The thread size on the Amals, points cover and gearbox inspection cover are #2 BA.

Sorry I read the thread but missed the most relevant part about most cycle parts are UNF, thank you for the follow up, I appreciate it, Rhys.

 

[Hobot]

The experts that are most up on this are the still remaining vendors, world wide, that often have an associated restoration business too. So after ya determine a thread form have fun choosing who to pay for proper screwing satisfaction. Btw out of reflex if it don't turn w/o a grunt of effort or whine of damage, I torch snot out it &or impact it. I have learned the scope of thread history a few times over the last 2 decades but dylexia rusts it away time and again.

Gotta love brit humor naming a top end tool set after owner's bull dog King Richard's, nick name. I'll add Metrinch to the no regrets buying thread. When I was in England the decent mechanics all wore a colored classic shop/lab coat, not casual shade tree grimy clothes. Impressed me until the class system details set in to be a sign of grimy hands servant class.

Btw vendors have thread chasing files, which I've used so wonder if anyone thinks worthwhile and can actually match up file face to threads that need it, the first time? IIRC files stamped with main thread forms sizes to know about. Keep oiled in case the next guy has high hopes too.