Thread Pitches

David Hughes

New member
As an aside, the Volunteer Fire Department I belong to owns the 1852 hand pumper "Papeete". We have had her since 1859, and she was in active service until 1931. Both Papeete and Monumental (the second hand pumper) pumped in the Columbia fire of 1920. When she was restored in 1959, when they started to reassemble her, every nut (they finally noticed) was mated to a specific bolt. All the threads were hand-cut. After many trials, the right nuts were mated to the right bolts, and index marks (center punch marks) were added to the pairs.

For better or worse, I recently found out I am the last member who knows how to work on Papeete. A beautiful machine, but 1852 technology, with her own tricks and procedures, passed down verbally from the old days. You have to live where you work, so my profile says Davis, but my heart is still in Columbia. Last Fire Muster, she pumped 131 ft, beating Sonora (with the 1876 "Eureka"), who could only pump 123 ft, and my life was complete
 

beezerbill

Subscriber
Because of my optics work I know where to buy taps for 1/4-80 3/16-100 and 1.035-40 among others.

BTW as far as I can tell there is no standard for plastic bottle threads such as coke or water bottles.

“The wonderful thing about “standards” is that there are so many to choose from!"
1.035-40. Sounds like Thorlabs. They also have 2.035-40. I frequently have to singlepoint turn these and other oddball optics threads.

I also had to make a brass cap for a NAPA brand ATF plastic quart bottle so I could pressure-feed fluid to the transmission directly out of the bottle. The thread pitch varied over the length of the thread! I just took the average of the pitch, figuring that the plastic had enough give, and it worked just fine.

And don't forget some of the British threads with their odd thread angles - 55 degrees for Whitworth and I recall 47.5 degrees for BA threads. Also, BA thread pitches are really weird.
 
.In the 70s i had a friend who owned a small screw manufacturing company in New Hampshire. They made the screws used in Kodak cameras. They were given the specs from the customer and the set up their machines to make these micro fasteners. They fed the specified metal rods into them and out came the finished product at a very rapid pace. AL
 

bartlett0815

New member
A few days ago I received yet another gun I don't need, a 1871 Snider Enfield MKIII military prison shotgun. The gun needed new sidenails, which are the bolts that go through the stock to hold the lock on the right side. I am told that the Enfield threads are 27 and 1/3 TPI. Since the bolts only have about 1/4" of thread engagement I cut 27 TPI a little loose so they fit. I had to use my old South Bend lathe since my new lathe doesn't have a setting for 27 TPI.

Kevin in NC
 

beezerbill

Subscriber
.In the 70s i had a friend who owned a small screw manufacturing company in New Hampshire. They made the screws used in Kodak cameras. They were given the specs from the customer and the set up their machines to make these micro fasteners. They fed the specified metal rods into them and out came the finished product at a very rapid pace. AL
That wouldn't per chance have been Central Screw in Keene? They were a large manufacturer, I recall they had a record of something like 6 million fasteners in one day. They made hardware for three of the four auto manufacturers in this country at the time but I forget which three.
 

kwfiggatt

New member
I work with at a place where we have equipment from all over the world. The worst thing for me are metric/ISO/BSPP/BSPT vs NPT pipe threads, especially if the heritage of the equipment is somewhat unclear...

Try to measure 1/8"-27 NPT vs 1/8"-28 BSPT and 1/4-18 NPT vs 1/4-19 BSPT on used fittings where the threads are slightly stretched. Sometimes something gets a lot of dope and a lot of torque... :D

Another weird one are "Enots" fittings used on a British dyno. These are 7mm-1.0 thread sized compression style tube fittings for hydraulic lines where the compression fitting is cut into the body of the part. The tube nut and compression ferrule get threaded into the part. Was fun figuring that one out... :bonk:

Kevin
 

TekNik

New member
I have seen where nuts of the nominally correct size sometimes will not fit on bolts that are the same size and have the same thread pitch. Typically the nut will be able to bounce in the thread or the nut cannot be run on by hand.

Sometimes this happens with clean, new hardware.:rant:

TekNik
 

DustyBar

Subscriber
I worked for Butler Mfg and years ago we had metal building brace rods threaded in such a way that a nut designed to be used on them could not be threaded onto an A325 bolt but the A325 nut would work on the rod. I believe the threads were rolled onto the rods. I know the pitch and size could be the same but maybe the class fit prevented a low grade nut from being used on a high strength bolt.
 

cobbadog

New member
In rebuilding the engine on our Pommy David Brown Cropmaster tractor all went well until I found an issue with 2 nuts on the big end bearing caps. Owning a few Pommy tractors and mowers I have a fairly good array of both BSW and BSF taps and dies to clean up threads. Out with the thread gauge and it was 5/16" x 27 ( I think) but after looking on the thread chart it was BSB, brass pitch on a high tensile nut and bolt.
Simply brilliant, not!
 

M.Canute

Member
As a mechanical designer I run into odd threads on a regular bases. Just some examples.
Davenport screw machines have there own thread about the same size as a #10

miniature toggle switches are 1/4-40

The optics industry has many odd threads. A microscope thread MAY be .8 x 36 Whitworth form

Then there is the "standard" C mount lens thread (1.0-32)

Because of my optics work I know where to buy taps for 1/4-80 3/16-100 and 1.035-40 among others.

BTW as far as I can tell there is no standard for plastic bottle threads such as coke or water bottles.

“The wonderful thing about “standards” is that there are so many to choose from!"
Here are some standards for them. https://www.bevtech.org/threadspecs-downloads.asp
 

Brian Triebner

Subscriber
Just started working on another engine and found a 13/16 X 14 tpi, called my machinist friend and he can get me a tap in 10, 12, 16, 18, 20, 24, 30, and 32 tpi but not 14 , strange.
 
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