Title tells it all. How does one tell the difference? Thanks :sos:
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Title tells it all. How does one tell the difference? Thanks :sos:
Just about every part is different; sometimes subtly, often not.
Manufacturer's marks for starters. Then the obvious stuff like furniture, muzzle devices, gad blocks, sights, dust covers, gas plugs, extractors, cocking handles, butt-plates, etc.
One interesting thing, however is that during the development of the "inch" pattern, a lot of effort went into retaining a lot of component dimensions. You can plug an Inch "upper" assembly onto a Metric "lower" / TMH and it will work. The threads on the screws are different, but VERY close. The rear-sight windage screws are ALMOST identical; not surprising, as the VERY "British" BA thread series is actually derived from the old Swiss "Thury" metric clock-makers thread system. For example, Zero BA has the same pitch as M6, but EVERYTHING else about it is different.
NEVER try to force ANY thread when assembling either system. If the mating surfaces look unmolested, and the right size, but do not run all the way relatively easily, STOP. You may have the proverbial "mixed bag". Breech thread? 16 TPI and 1.5mm pitch are "close", but I'd advise against trying to fit one into the other, especially with the aid of valve-grinding paste and / or big wrenches with four-foot "cheater bars".
There are several good books that detail all of the differences, but original "works" drawings are MUCH harder to find. There is also a "spectrum" of web-sites that deal with these matters to varying degrees of competence.
The whole headspace / locking shoulder caper is the big choke-point, even if you have all parts of the correct pattern. If your assembled rifle fails headspace, ( and this is NOT the same as SAAMI "sporting" spec), you need to find a gun plumber who is FAL / L1A1-savvy AND who has the tools and gauges (and a goodly collection of the full range of the shoulders), to go with it. I understand that there are a couple of such gentlemen who frequent these pages.
Yes, but in practice the two threads will fit together fine, without needing to be forced together. When I last measured the external diameter of a 0 BA thread it was 6mm diameter.Quote:
Originally Posted by Bruce_in_Oz
well...since no one gave the smart a%* answer, I will
if the number has an abbreviation with an m in it, it's metric. all else is standard.:dancingbanana:
Yep! That Zero BA diameter detail seems to have missed "publication" in my first post.
The other very British" thing about BA threads is the size relationship:
To get the dimensions of a size say, 1 BA, multiply the previous larger size (Zero) buy 0.9. Ditto all the way down.
Had to be something to do with manual gearbox lathes that could be adjusted in those multiples. For us mature chaps, the original Meccano screws and nuts were all BA, Apparently, when the French took over, they changed to the nearest metric thread.
And then, there are "Enfield" screws; bearing no resemblance to any other on the planet. From the Martini Henry to the last No1 Mk 6, and including the P13 / P14, all were held together with "Enfield Specials", except the Lee Enfield stock bolt, which is 7/16" Whitworth. Then, there are the VERY British "Admiralty" threads, as used by the entire Japanese civil and military ship-building industry until fairly recently.
Mausers up to the M98 and the Type 30 and 38 Arisakas are full of Imperial threads, not so much the Type 99.
There is also a range of "aerospace / aeronautical" screws that have a simi8lar "form" to BA; apparently a good thing when bolting together components made from Aluminium alloys.
Well, I got what I got. The only thing going into the future is, will any mag fit (inch or metric) and lock into this firearm? Thanks.
No, but metric mags are said to fit imperial rifles but not the other way round. I've never tried it.Quote:
Originally Posted by Rockandroll
That IS correct. Metric mags have such a small front projection, just a small sliver. Inch mags have a large steel nose projection to lock them in place. You can put a metric mag on an inch gun and it will stay but could come loose. An inch mag will NOT fit a metric gun without mod of either the mg or the upper.
Inch mag left, metric mag right.
deleted -due to duplicate info posted 1 minute after BARs post. My timing has been like this lately- Go figure?
Thanks guys. I’ll dig my mags out of long term storage and check them.
Quote:
Originally Posted by Bruce_in_Oz
Bruce, that's not actually correct.
1BA is 88.333% of 0BA diameter, 2BA is 88.679% of 1BA diameter, etc - and it doesn't follow in a linear scale on pitch either.
BA is a weird thread, as despite the 'British Association' name, it is actually a Swiss thread, and metric thread form.
---------- Post added at 05:50 PM ---------- Previous post was at 05:46 PM ----------
Quote:
Originally Posted by Flying10uk
M6 coarse and 0BA are indeed 6mm dia x 1mm pitch.
HOWEVER, interchange them at your peril, they couldn't be more different.
M6 coarse is 60 degree thread form, 0BA is 47.5 degree thread form.
Interchanging them is NOT a good idea!
...I don't think it's your timing...he is very fast :)Quote:
Originally Posted by Salt Flat
David.
I am familiar with the differences in form. BA was derived from those Metric Thury watchmakers threads, the form and included angle of which are unknown to me, but can probably be found on the wall-charts in half the alpine workshops in Switzerland.
Weird (like "Enfield" threads) works, but it can be a pain.
Here's a BA comparison chart:
BS 93 British Association (B.A.) Screw Threads Data Charts
My first car was a 1950 Vauxhall Wyvern. Made for the "Commonwealth" market, nevertheless, it contained a LOT of US "unified" threads. The catch was that a lot of the bolt-heads and nuts associated with these UN threads were WHITWORTH, so that "imperial" mechanics could work on them with their usual wrenches.
All depends on how much torque is put on the nut/thread.Quote:
Originally Posted by David TS
If memory serves me correctly 2BA will fit 3/16 B.S.F.
---------- Post added at 12:51 AM ---------- Previous post was at 12:43 AM ----------
A story that I heard was that BSW dropped a spanner size on all it's threads, making it the same as B.S.F. spanner sizes, during WW2 in order to save steel. How true and how much steel was saved I don't know but it does give one explanation as to why one encounters 2 sizes of B.S.W. nuts/bolts.
It isn't a matter of how much torque is put on it, it is just bad engineering practice, and an easy way to ruin a thread, which wouldn't be a good outcome on an internal thread.Quote:
Originally Posted by Flying10uk
And mixing BA and BSF are again bad practice, 47.5 degree thread form vs 55 degree thread form.......
David I don't know how much practical experience of thread and screw cutting you actually have.
Perhaps you have access to a vast stock of obsolete screws and nuts of every imaginable size and every conceivable thread, not all of us do.
Therefore, if I don't have the exact size required to do a particular job I may look for another way round the problem. That my mean making a screw on my vintage lathe by cutting the thread or it may mean using something else that is similar and will do the job.
I don't make a habit of tightening up screws/bolts so tight that the thread strips.
2 threads to be careful of are 1/2" BSW and 1/2 UNC because there is 1 t.p.i. difference between the 2 and try mixing them and you'll strip the threads, even though the threads are close enough to look the same visually.
Quote:
Originally Posted by Flying10uk
My experience? My dad was a toolmaker and watch repairer and taught me much, and I started my electronics and engineering apprenticeship with Marconi way back in 1969. After school I worked in a number of production machine shops, and small auto repair workshops. Wind forward to today, I have just built a new 400 sq ft workshop, which houses two Colchester and one Harrison lathe (all screw cutting), three milling machines, and various other sundry machine tools. I have also accumulated a large stock of BA, UNF, metric, Whit, BSF and cycle fasteners over the years.
I don't say the above to brag, but rather to simply answer your question.
So whilst I do have access to a number of fasteners, or the ability to make them, one thing I will not do is fit mismatching fasteners together, my head will just not allow me to do it! ;)
Interesting how a simple question morphed into a detailed discussion of pitches, threads, acronyms, diameters and similar big words related to screws, but tending to the arcane if not more mysterious words.
Yep...Quote:
Originally Posted by Daan Kemp
"I have also accumulated a large stock of BA, UNF, metric, Whit, BSF and cycle fasteners over the years."
With 400 sq ft available! Try harder. :D
"I don't say the above to brag..." Neither do I :lol:
But to the above list I can add such quaint items as Panzergewinde (German conduit thread), British conduit, BSP, NPT, ACME, ME, UNC, UNEF, metric series 1mm, 0.75mm, 0,5mm and some oddballs (like multi-start taps) that really puzzle me.
I learnt a long time ago to keep all machined thread items (nuts, bolts, spindles...) from every piece of dismantled equipment that I could get my hands on.
Motto: it might come in handy one day. 99% will probably never be used, but the usable 1% is priceless.
- Of course, the trick is to find it when you need it!
But if you want to refurbish old rifles (back to 1670 to date) then you need to be a bit flexible about things like thread forms.
Today's useless information: did you know that the barrel thread for a Luger pistol is 18mm diameter x 20 tpi? Eat that, standards fanatics!
I suspect that the reason for the presence of "Imperial" threads, especially thread pitches, in Mausers, Arisakas, Mosin Nagants, (and Lugers) was that almost all of the machinery used to make such things was initially from British manufacturers.. See also the rapid rise of US tooling and machinery from folks like Whitney and companies like "Bridgeport" and "Cincinnati".
The entire Japanese ship-building industry used the very British "Admiralty" thread system until VERY recently, and the probably still have the capacity to turn out the appropriate fittings to keep someone's rust-bucket afloat for a few more years.
The Imperial Japanese Navy was totally modeled on the Royal Navy, right down to the nuts and bolts and "mess traditions", with about the only significant difference being the issue of Sake instead of rum.
Yes, this is what I am implying and it's the same with any hard to find thread for obsolete machinery.Quote:
Originally Posted by Patrick Chadwick
I would suggest that with a small size screw such as 3/16" B.S.F. and using a 2 B.A. nut, if the correct one isn't available, as a "work-round-solution" because even though the thread angle is different, the actual missing metal from the mating threads is tiny. This is because the difference between the 2 thread angles is only a few degrees over the height of the thread. One could work it out if one wished but the result would be a tiny amount of metal missing from the mating threads.
Ok Patrick, I will happily defer to you on this one ;) :lol:Quote:
Originally Posted by Patrick Chadwick