A thread with a thread question

[Atlas Commando]

I need to clean up the threaded holes in my barrel. The stud part number is NMT2161. It seems like the threads measure at 24 tpi, National Coarse. Can anyone please confirm the size of tap I need to do this correctly? I can start a tap in, probably just hitting resistance due to the corrosion, but would like to get some backup before forcing it further.
Thanks very much for your time!

 

[L.A.B.]

The stud part number is NMT2161. It seems like the threads measure at 24 tpi

5/16" x 26 CEI/BSC

https://www.oldbritts.com/nor_comm_69_6.html
"NMT2161 Stud, 5/16 x 26, Cylinder Head"

 

[Atlas Commando]

Thank You Sir! I am glad that I asked before getting rammy. That's a tap I don't own, time to buy one.

 

[rvich]

If it is a matter of cleaning corrosion or old sealant out of the threads you could take an old stud and use a Dremel or hacksaw to cut a slice parallel to the length of the stud. When you run it in the old gunk collects in the slot.

I've repaired slight damage to bolts and studs by doing the same with a nut.

 

[joe czech]

(my 2-cents, FWIW) be careful - whitworth threads differ from unified national standard. I agree with the above - run a thread chaser and not a thread cutting tap into an existing hold. never seen british whitworth taps, either cutting or chasing, so as stated above, use an old whitworth bolt, and use a Dremel to make one. by no means an expert on whitworth, but the thread profile is different from unified national fractional. whitworth is 55° and has smooth or blended threads vs 60° sharp "V" cut threads for UN.

good reading - https://www.rustmag.com/gear/2018/1/4/threads-and-thread-systems

 

[L.A.B.]

(my 2-cents, FWIW) be careful - whitworth threads differ from unified national standard.

Indeed they do, however, CEI/BSC isn't 55 degree 'Whitworth' thread.

https://www.gewinde-normen.de/en/cei-thread.html

unified national standard

UN = Unified.
https://www.ring-plug-thread-gages.com/ti-N-vs-UN.htm

"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.


Some confusion over the UN designation exists. Some people think it means Unified National based on the fact that three national entities came together to unify their thread standards; thus: Unified National Screw Thread Form. By reading the B1.1 this is not supported; rather UN is the abbreviation for UNIFIED. In the B1.1 the thread is called either Unified Inch Screw Thread or Unified Screw Thread with the preference being Unified Inch Screw Thread to indicate the unit of measure used in the screw thread series."

 

[joe czech]

OK, now, i'm really confused....

guess i need to get up to speed on the nuts and bolts end of these things. sure glad I said " by no means an expert " -

 

[L.A.B.]

OK, now, i'm really confused....

No need for confusion if the following is remembered that not all 'British' threads are 'Whitworth', also....

From the previous link:

"1. The N-series thread is obsolete.
2. The N-series screw thread was replaced in 1949 with the UN-series.
3. The NC-2 thread call-out should now read UNC-2A.
4. The N-series is fully mechanically interchangeable with the UN-series.
5. The difference is only 0.0001 to 0.0002 of an inch on the pitch diameter.


SUMMARY OF DIFFERENCES
There are obvious changes between the N-Series and the UN-Series. First, the thread nomenclature was changed from N to UN. This was necessary to designate the internationalization of the Unified Inch Standard Series screw thread. Second, the male and female threads have received individual alpha designations: A = Male; B = Female. Third, the pitch diameters of the threads were adjusted. The class 2 thread pitch diameter adjustment allows for an allowance between the male and female threads. In other cases the pitch diameter were changed to remove tolerance issues which made the threads nearly impossible to manufacture and gage. Within the now obsolete N-Series some product pitch diameter tolerances were practically absorbed by the combined tool and gage tolerances leaving little working tolerance for the product manufacturer. Finally there were several other minor changes made to the general thread form of the end product conform to manufacturing realities and some benign changes were made relating to the major and minor diameters.

INTERCHANGEABILITY
What did not change was interchangeability with previous versions of the screw thread. The UN-Series is fully backward compatible with the N-Series. This is codified in ANSI/ASME where the authors of the standard, in several places, remind the reader that the N-Series is mechanically interchangeable with the UN-series. The first sentence of the Foreword to B1.1:2003 is their strongest move to eliminate the N-series screw threads once and for all."

 

[lcrken]

Just order up a BSC 5/16-26 tap from one of the online suppliers, like this one

https://britishfasteners.com/index.php/taps/bsc-cei-taps.html

Or just buy a full BSC tap set from one of the many online suppliers, at Amazon and elsewhere.

Ken

 

[ashman]

After working at a TEC college (TAFE) for 31 years and 15 years in the maintenance workshop when they decided to move the machining shops to another college they closed the maintenance shop down and I was lucky to get all the tap and die sets that had been used over the years, so have everything needed for my British bikes, Norton included, metric for my Honda and also came in handy for the Shovel Head Harley I am building, and have helped a few mates out with cleaning old threads out, lots of threads I don't use but I have them if someone needs them.
The best thing is they are all good quility no cheap Chinese knock offs.

Ashley

 

[joe czech]

No need for confusion if the following is remembered that not all 'British' threads are 'Whitworth', also....

From the previous link:

"1. The N-series thread is obsolete.
2. The N-series screw thread was replaced in 1949 with the UN-series.
3. The NC-2 thread call-out should now read UNC-2A.
4. The N-series is fully mechanically interchangeable with the UN-series.
5. The difference is only 0.0001 to 0.0002 of an inch on the pitch diameter.


SUMMARY OF DIFFERENCES
There are obvious changes between the N-Series and the UN-Series. First, the thread nomenclature was changed from N to UN. This was necessary to designate the internationalization of the Unified Inch Standard Series screw thread. Second, the male and female threads have received individual alpha designations: A = Male; B = Female. Third, the pitch diameters of the threads were adjusted. The class 2 thread pitch diameter adjustment allows for an allowance between the male and female threads. In other cases the pitch diameter were changed to remove tolerance issues which made the threads nearly impossible to manufacture and gage. Within the now obsolete N-Series some product pitch diameter tolerances were practically absorbed by the combined tool and gage tolerances leaving little working tolerance for the product manufacturer. Finally there were several other minor changes made to the general thread form of the end product conform to manufacturing realities and some benign changes were made relating to the major and minor diameters.

INTERCHANGEABILITY
What did not change was interchangeability with previous versions of the screw thread. The UN-Series is fully backward compatible with the N-Series. This is codified in ANSI/ASME where the authors of the standard, in several places, remind the reader that the N-Series is mechanically interchangeable with the UN-series. The first sentence of the Foreword to B1.1:2003 is their strongest move to eliminate the N-series screw threads once and for all."

if not all british threads are whitworth, then HOW do I determine the thread type used on my 74 commando - BSF, BSC-CEI, BSW, ??? i understand the coarse/fine thread thing, but the rest of it - also, i'm seeing a numbering system like 0, 1, 2, 3, 4 BA - what is a 4 BA? kind of a brit bike noob, and this may sound like a dumb question, but in general, if I have to replace hardware, how do I source the correct hardware? is there a standard listing somewhere?

sorry for my first post, but I assumed everything used on old brits was whitworth thread. my bad - I really need to study up on the subject.

 

[Atlas Commando]

After working at a TEC college (TAFE) for 31 years and 15 years in the maintenance workshop when they decided to move the machining shops to another college they closed the maintenance shop down and I was lucky to get all the tap and die sets that had been used over the years, so have everything needed for my British bikes, Norton included, metric for my Honda and also came in handy for the Shovel Head Harley I am building, and have helped a few mates out with cleaning old threads out, lots of threads I don't use but I have them if someone needs them.
The best thing is they are all good quility no cheap Chinese knock offs.

Ashley

I could drop in and borrow a tap maybe, but that 16 hour flight is tough....

 

[Atlas Commando]

So having digested all this (and getting a mental image of L.A.B. sitting in the captain's chair of a starship, surrounded by British motorcycle reference material and ASME codebooks) I think I'll try the 'dremel a groove' trick first. I'll order new fasteners which is a good idea since these are crowding 50 years old and who knows how many times they were stretched. Then I'll use a guaranteed correct fastener to pull the right size from my scrap heap. If it works, it's cheap. If it doesn't work, I can buy a single correct blind hole tap. I thought about buying a set of British taps Ken, but this is quite possibly the last or second last British motor I'll build.
What a resource this site is! Although, I am remiss since I neglected to do a search before simply asking my question. I don't want to chew up peoples' time answering things when the information is already out there.

Thanks everyone for your responses!

 

[L.A.B.]

if not all british threads are whitworth, then HOW do I determine the thread type used on my 74 commando - BSF, BSC-CEI, BSW, ???

By learning what's what, although there are part number charts that can be used to help with thread identification.
Some but not all, thread forms were also changed from British Standard to Unified during Commando production.

Here is one 'identify by part number' list (these lists do contain the odd error)
Link deleted as it no longer works.

but the rest of it - also, i'm seeing a numbering system like 0, 1, 2, 3, 4 BA - what is a 4 BA?

BA = British Association. A 47.5 degree thread often used for fasteners under 1/4".

British Threads - BA

britishfasteners.com

https://en.wikipedia.org/wiki/British_Association_screw_threads

kind of a brit bike noob, and this may sound like a dumb question, but in general, if I have to replace hardware, how do I source the correct hardware? is there a standard listing somewhere?

This is what I mean by knowing your threads as a Commando can have a mixture of UNF, UNC, UNEF, UN, CEI/BSC, BSW, BSF, BA, ME and BSP threads depending on the actual component and time of production, plus spark plugs and spin-on filter threads are metric (also speedo and tacho cable upper end fittings and 850 Mk3 switch cluster screws).
(Edit: Possibly also UNS but would be for lock ring threads, access plugs, etc.)

 

[joe czech]

By learning what's what, although there are part number charts that can be used to help with thread identification.
Some but not all, thread forms were also changed from British Standard to Unified during Commando production.

Here is one 'identify by part number' list (these lists do contain the odd error)
http://stainlessbits.com/link12a.html




BA = British Association. A 47.5 degree thread often used for fasteners under 1/4".
https://britishfasteners.com/threads/index.html

https://en.wikipedia.org/wiki/British_Association_screw_threads



This is what I mean by knowing your threads as a Commando can have a mixture of UNF, UNC, UNEF, UN, CEI/BSC, BSW, BSF, BA, ME and BSP threads depending on the actual component and time of production, plus spark plugs and spin-on filter threads are metric (also speedo and tacho cable upper end fittings and 850 Mk3 switch cluster screws).
(Edit: Possibly also UNS but would be for lock ring threads, access plugs, etc.)

"time of production" - - are you saying a early 74 could have different hardware from a late 74? if so, with all the different thread types, how do you folks keep things straight? is it safe to assume if I order a part from someone like oldbritts.com - say p/n 60348, hex nut, 5/16 X 24, I would get the correct fastener for my application, or am I putting too much thought into this? BTW, thanks for the stainlessbits.com link.

 

[L.A.B.]

"time of production" - - are you saying a early 74 could have different hardware from a late 74?

1974 is OK, the more significant changes occurred around '71/'72.

if so, with all the different thread types, how do you folks keep things straight? is it safe to assume if I order a part from someone like oldbritts.com - say p/n 60348, hex nut, 5/16 X 24, I would get the correct fastener for my application, or am I putting too much thought into this?

If you order by part number then you should be fairly safe as the part number changed when the thread changed although you may be supplied with 60 degree UNC fasteners instead of 55 deg. Whitworth although there aren't many actual Whitworth fasteners on a '74.

A vernier caliper and sets of Whitworth and Unified pitch gauges (plus it's useful to have metric and if possible, BA) make identifying fasteners much easier.

 

[L.A.B.]

Hexagon size can also help to identify if a fastener is Unified or not.

http://www.sat.dundee.ac.uk/~psc/spanner_jaw.html#Jaw_Size_Table

However, when in doubt...ask.

 

[ashman]

Good set of thread gauge is worth while to have in your workshop, when I got all the tap and die sets I also got the wall charts with all thread sizes, pitch and drill sizes needed for each tap, I also have a full set of thread files which also comes in handy. I have everything covered.

Ashley

 

[gortnipper]

By learning what's what, although there are part number charts that can be used to help with thread identification.
Some but not all, thread forms were also changed from British Standard to Unified during Commando production.

Here is one 'identify by part number' list (these lists do contain the odd error)
http://stainlessbits.com/link12a.html

I think @marshg246 has a more up to date list with some of the errors (not all) corrected on his site at http://www.gregmarsh.com/MC/FastenersList.aspx

https://www.accessnorton.com/NortonCommando/british-motorcycle-fasteners.21959/#post-327986

 

[dynodave]

"time of production" - - are you saying a early 74 could have different hardware from a late 74? if so, with all the different thread types, how do you folks keep things straight? is it safe to assume if I order a part from someone like oldbritts.com - say p/n 60348, hex nut, 5/16 X 24, I would get the correct fastener for my application, or am I putting too much thought into this? BTW, thanks for the stainlessbits.com link.

If you can follow this "general" trend then as LAB said, it is based on the production period.
Virtually all pre commando is British thread of some variety.
Then when a component was made, as if new for commando, it would have usually been converted to UN threads. Generally all rolling chassis items are UN. Front triple trees, axles, lug nut hubs on first series commando are UN(S) where featherbed was all British of a similar type. Many Atlas and early commando components are confused for this reason.
Engines 20M3 was followed by 20M3S then 200000,then 300000 then 325000. The engines incrementally used more UN threads each time a newer version was made. Note the head and barrels stayed British to the end. It is a very similar story for the AMC gearbox. The primaries were new for commando, so generally UN.
I usually tell folks to get BSW, BSF, and CEI taps and dies, if needed, but it is mainly for the engine and gearbox.
The use of metric is VERY small and only for some particular reason.
The use of BA screws instead of american numbered hardware seems to be pretty consistent. I have never found a #10 american where a 2BA is actually used.