Technical Oddball NF(?) Thread pitch nut

Hey Guys!
Am in the throes of refurbishing my AV8's "SAFEGUARD" brand 6 volt motor-driven horn. As the diaphragm on it was rusted through, I was able to adapt a replacement Model "A" one, save for the metal piece mounted near to the middle which has a raised "dimple" which engages with the concave dimples in the small wheel attached to the end of the motor's armature. The "A" piece had an end shape like that of a slot-type screwdriver but with a little "backyard hotrod ingenuity", I was able to come up with something that while perhaps not having the metal hardness of the original piece, should work fine (at least for a while - crossed fingers!). My only problem now is finding the proper thread nut to lock the "concave dimple" wheel on the threaded armature shaft end after I've figured out it's correct height to engage it with the diaphragm dimple so it produces the proper rate of vibration to make the sound (Whew!). There was no locknut on it when I took it apart which I found rather odd! I've stumped our biggest local fastener supply outlet. It's a fine thread, but not National and, I believe, not metric as it is a U.S. made unit approximately late 20's/early 30's. The counterman said nearest he could figure was around an 8-40. I've looked at several online charts but to no avail. Any thoughts from you machinists or fastener gurus as to what it might be? Many thanks in advance! Regards, Dave.

 

Maybe British standard ( I think that's what it's called).

I have an OT British Seagull outboard motor and that's what was used on it

 

Thanks upspirate! Now that I think of it, I recall British Standard coming up the odd time at the shipyard I worked in. Will have to check that possibility out. Regards, Dave.

 

Some British cars' fasteners are "Whitworth".

 

BSW is British Standard Whitworth.

 

Try British Association thread.

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

 

I suspect Whitworth as discussed


Sent from my iPhone using The H.A.M.B. mobile app

 

The Machinerys Handbook is your friend, pretty dry reading but EVERY question on this subject can be answered within.

http://www.barnesandnoble.com/w/mac...dition-toolbox-edition-erik-oberg/1105608485#

 

Thanks everyone for your input! I put my "Made in England" vernier on it and it comes out at bang on 5/32" O.D.. Looked over some BSW charts but didn't see anything that might be close. Don't have any thread pitch gauges fine enough, and certainly no British Standard Whitworth ones. As I mentioned before, the horn was U.S. made but I guess anything is possible! I may have to invest in the Machinerys Handbook as DDDenny suggested! Regards, Dave.

 

did you try a 8-40 nut?

 

It is likely one of the old USS (United States Standard) threads.They used for instance 1\4X24 and 1\4X30 tpi.It was pretty common to run into this on pre war American Vehicles.HD used it in some applications up to 1977! In your situation I would likely run a #8 NF die on it and install a nice,new #8 NF nut. Whitworth threads use a 55 degree thread pitch all ours are 60 degrees so they do not interchange well even if the TPI is the same.

 

http://www.tstool.com/default.aspx?page=item detail&itemcode=ST8-40 There is an 8-40 tap for you. About $8 I have yet to find a thread they don't have a tap for.

 

Haven't found one so far tb33anda3rd, and at this point I don't even know if there is such an animal. Thanks for your reply! Regards, Dave.

 

How about a hard plastic nut? Maybe the stud would cut threads into a piece of hard plastic. Shouldn't take much force to hold there.

 

Aha! Another obscure fastener possibility! Thank you steinauge! I would need a #8 tap as well as the dimple wheel is also threaded, but no sweat. I will investigate further!

 

Well I'll be dipped in shit! There it is! Many thanks enjenjo! Will try and verify the thread count on the shaft just to be sure but will definitely bookmark that site. Thanks again! Regards, Dave.

 

The pre 70 Harley Davidson used a lot of 1/4 x24 fasteners in the engine covers and lifter block areas. Colony and Garner-Westcott company might have something that would work out.

 

Now there's a possibility BamaMav! Will look into that. Thanks! Regards, Dave.

 

Thanks for that Slicklll - will check them out! Regards, Dave.

 

One quick way to check a thread pitch is take a screw with a known pitch ( in this case a #4-40) and try and mesh the two threads together side by side. If they are the same they will interlock.

 

Wont be a BSW (British Standard Whitworth) That thread profile was coarse.
Could be a BSF (British Standard Fine)
I had a mid 30's Morris car, and it had them..
They were very close to UNF/NF thread, but didn't like each other..

 

I thought I was pretty Bad Ass for having 1/4"-32 and 13/16"-16 taps.
They are for very common uses on our cars, but seldom need to be used.

Any guesses?

I also have a 1/2"-28 tap, but am not sure why. I think I know, but will have to check it out to be sure.

DDDenny, Machinery's Handbook is INVALUABLE!!!!! I just wish I understood 1/4 of what is in there.

 

Be sure to let us know what you find out / do in the end

 

Could be a Cycle thread - used a lot in the motor accessory industry;

http://motalia.com/Html/Charts/cycle_chart.html

I think the nylon nut is the way to go - cheap and easy to find

 

That's the nice thing about standards - there are so many to choose from.

 

Lots of "standards" within certain industries as well as individual companies.
I machined parts for the wood products industry for 30 years and it took a long time to understand why we did some of the things we did.
One of our older machinists told me its simple to understand; for every part the customer can buy at the hardware store that's one lost company replacement parts sale.
When I first started I made a large batch of fine thread shafts, one inch right hand threads on one end and left hand threads on the other end with a knurled section in the middle, the stock was inch and a half diameter by about twelve inches long so there was quite a few hours in them. Got them all done and about an hour later the leadman comes back with them and says "you fucked up this order".
Come to find out, there were two "standard" one inch fine threads, 12 tpi and 14 tpi.
He made ME go to the engineering department to get the print changed to call out the threads per inch instead of just saying fine thread. Engineers don't take kindly to being told by a machinist they "fucked up", especially a young machinist.

 

Electrical threads are odd ball, like an 8-36, 6-40 and so on. If you can tell how many threads are in a 1/4", multiply that x 4 and you know the TPI (threads per inch). I don't think NEF (national extra fine) threads go that small. If the male thread measures 5/32", you most likely have a #8 thread, probably an 8-36 UNF.

http://machiningproducts.com/html/UNC-UNF-UNEF-Thread-Dimensions.html

 

Thanks wayne-o! I did actually try that but couldn't come up with a match from what I have. Regards, Dave.

 

Years ago I remember hearin' talk about fine pitch, coarse pitch, and sonova pitch.

 

UPDATE: Tried a photo but the clarity sucks! Attempted to figure out the threads per inch (and I am definitely NOT a math wizard!). Only 3/8 of an inch of the end of the 5/32" armature shaft is threaded and in that length I counted damn near sixteen threads (just a pussy hair shy of being bang on 16). So, to my mathematically-challenged brain that puts it somewhere in the 36 to 40 TPI range. Sound about right?? Thanks to everyone for your input! Tomorrow, I will try some bike, motorcycle and electrical suppliers to see if they have anything. Stay tuned! Regards, Dave.