Unusual thread? well it is to me!!

Son came round yesterday with the carburettor from his seagull outboard, the banjo housing threads were stripped that connects the floatbowl to the body, the brass banjo bolt ok just the alloy body stripped, no problem says I, I'll turn a mandrel & mount it from the other end so it's concentric with the slide & I'll bore it out & loctite a bronze sleeve in & threadcut it in the lathe,then I tried to identify the thread, it's 5/8 x 24 tpi, looking through my charts in various books/zeus etc & finally found it in my machinerys handbook which states it as "unified & american standard fine & extra fine series,it is the extra fine series, what puzzles me is it's a british seagull motor & an amal carburettor, perhaps its another thread? I remember reading in ME an article about seagulls.

Back in the late 60's to mid 70's there was a serious move to use American threads such as UNF and AF in the UK motor industry........some classic Jags for instance are 'blighted' by parts with UNF threads. at the time it was thiought better to standardize with the US industry rather than Europe/metric.......Come to think of it, it might still happen!!......Oh no it won't we don't own any of our car factories now do we?

Hi Codger,

5/8" X 24 tpi is the thread on PL259 and SO259 RF plugs and sockets, commonly found on CB radios and the like.

Thanks for the reply John, I thought someone would have heard of it, [hmmnn must get the old "chicken box" out !!]

Pretty standard for carbs of this period.

Amals used 9/16" - 15 thou x 20 for their jet holders, tap one out with a standard 9/16" x 20 and they pull air in up the threads and won't run.

Still got the special tap.

Same as the military at one point, they fitted 14.2mm plugs in their vehicles to stop you pinching them and putting them in your cars and bikes, got that tap as well

Edited By John Stevenson on 07/07/2016 21:25:06

Weren't round teabags introduced by BR on this basis? Mind you, one MD of mine never bothered about minor theft, he said (Specifically about ball pens) that "eventually you reach saturation". This may have been OK for a small satellite communications company, but could otherwise have resulted in BR supplying half the nation with tea! AND the satcoms company went bankrupt...

Geoff

I have come across several odd 24 TPI parts that where from Naval parts. 1/2" 24 and 5/8"24 are also found on old motorcycles.

Transport always seems to throw up odd fasteners, like M7 on push bikes ...

Admiralty Fine Thread is a simple system for parts outside the normal nut'n bolt increments which pops up in many unexpected places.

Whitworth form 24 TPI under 1/2" diameter, 20 TPI from 1/2" to 3/4", 14 TPI from 3/4" to 1", 12 TPI from 1" to 2", 8 TPI from 2" to 4" and 6 TPI above 4". Last time I found one was on a cheapy Chinee compressor holding a non standard "not quite PCS" airline connector which needed changing to a standard one. No room to open out the female to a standard BSP so the thread had to be identified. Which drove me nuts until the penny dropped!

Another one to watch out for is large pipe threads in non pipe applications to get a finer thread than normal in that diameter.

Then there are the American industry standard specials and semi constant pitch series, mostly automotive and aeronautical. Which can drive you crazy as there are so many and around half of them aren't listed where you expect to find them. Machinery's Handbook and Guide to World Screw Threads aren't enough. Pretty much all officially obsolete post WW2 except they forgot to tell the users so filtering by date is less than reliable. Last one to get my Workshop Esperanto flowing was an obsolete in 1914 thread on a piece of equipment made in mid 1990's. Presumably the old "force you to buy OEM parts" trick. Which becomes a major pain when said parts are unobtanium.

Clive.

If you need any parts for Seagulls or have problems running them try "Saving old Seagulls" based just up the road from me in Tillingham.

What they do not know about Seagulls is not worth knowing

Not just on the PL259 and the SO239 (aka 'UHF connectors' ) but also on N-types. 60 degree ANEF profile. These connectors are used on lots of Amateur Radio & professional RF test equipment. They might also be used, wire-locked, on some avionics equipment, although Bayonet-C and BNC are favoured as being less prone to vibration induced uncoupling (Andrew to comment?? ).

I have also encountered, on the Amateur Radio market, UHF and N-type connectors with die-cast 'pot-metal' bodies with 5/8" diameter but 1 mm pitch thread. They look silver-plated and have red insulation. Cross-mating with the 'real' UHF & N-type connectors made by Amphenol and the like is a statistical nightmare!!!

Best regards,

Swarf, Mostly!

Funny this should come up when I spent the morning writing a report on connectors. BNC is too wobbly for avionics and introduces modulation on the signal so the threaded version TNC is used. Good for 18GHz while BNC is only used up to 1GHz. Odd that TNC Threaded NAVAL Connectors are used on aeroplanes.

Thanks for that valuable info Sam, I'll pass it on to my son, he has a couple of them [he loves them!!]

I take it Bazyle refers to the belief that BNC stands for "British Naval Connector" or perhaps "Bayonet Naval Connector". That's certainly what I was told as a lad.

Unfortunately I don't think it's true. The connectors were developed for military use by Messrs Neill and Concelman and are most likely named after them. Thus BNC is "Bayonet Neill Concelman" and TNC is "Threaded Neill Concelman".

I see the Neill Concelman theory has been promoted to truth by Wikipedia's BNC entry but does anyone actually know?

Feeling obliged to comment on this has left me worried that nowadays I'm both a first class nerd and a first class pedant! Sometimes it's a cruel world.

Cheers,

Dave

I sold my Seagull Century , purchased in 1960, 12 years ago; but still have & still use my forty plus bought by my father the same year.

Swarf, Silly... The N/BNC/TNC/C connectors were indeed named after their designers Neil & Concelman. I wrote an article for the Amateur Radio press on this basis, many years ago, and if you will allow me time, I will resurrect it for you.The idea is that, not only are they mechanically rigid & stable, but that they *look* like an ordinary piece of coaxial cable to the passing signal, ie., they are 'constant impedance' as well as coaxial. (Signal wire runs through the centre of a round, wire mesh, earthed screen) NB, red insulation on 'UHF' connectors is a No-No. Bin them! White insulation is better, preferably Nylon, or PTFE, but that connector is not a good one anyway, above about 30 MHz.

Geoff

Hi there, Geoff,

I'd be very interested to read your article but, re-reading this thread, I fear I've contributed to 'topic-creep'. If you can retrieve the article, I'd welcome receiving it as a .pdf file via PM.

Best regards,

Swarf, Mostly!

Me too please Geoff. It's possible I've already read it as I've been interested in Amateur Radio for many years.

Apologies for hijacking the thread from me too .

Thanks,

Dave

Edited By SillyOldDuffer on 08/07/2016 20:47:11

Geoff Theasby

I'd also be very interested to read your article.

Thanks in advance

Brian

Hi all,

I couldn't find it last night, it may have been on a computer since demised, although I kept the hard discs and can access them. I'll try again today, or at least find out who published it and when. Meanwhile, the Wikipedia entries are good, I even learned a few things myself!

Geoff