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What are these screws, and where can I get some?

Started by Stephen Furley, August 05, 2009, 09:54:31 AM

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Stephen Furley

I've got a problem with several 'restored' phones in that they've had inappropriate cords and transmitters fitted to them.  This generally means a poor quality modern cord , held in place by a knot tied in it.  Unfortunately, on the American 'phones this tends to mean that the screw inside the transmitter housing, to which the restraint on he handset cord is supposed  to be attached is missing; why can't they at least leave the screw in place if they're not going to use it?  The thread on these screws seems to be the same on WE 302 and AE 80, but it's not any thread that we have here.  Almost everything is metric here, though some small screws are still BA.  Does anybody know what size these screws are, and where I can get some.  Oldphoneworks have several sizes of screws, but I don't know if any of them are what I need.  My AE40 was also missing the spring contacts and screws for the original transmitter, but I managed to obtain a spare handset to get these from.

benhutcherson

I believe that they're a 4-40 screw. The 4 is a measure of the screw diameter, which translates to .112 inches, and 40 means 40 threads per inch. This is pronounced "Four fourtieths."

There's your lesson on American screws.

There will also be a length specified, which of course will also be in inches. I believe that for a handset cord restraint, you will want a 1/4 inch long screw.

So, you're looking for a 4-40 x 1/4" screw.

Stephen Furley

Thank you.  We used to lave loads of different threads here, but most of them are obsolete now.

foots

You're right about that Stephen, do they still use those odd British standard threads? I've worked on some JCB equipment several years ago that had that.
"Ain't Worryin' 'Bout Nothin"

Stephen Furley

Quote from: foots on August 05, 2009, 12:25:11 PM
You're right about that Stephen, do they still use those odd British standard threads? I've worked on some JCB equipment several years ago that had that.

BA (British Association) threads are still used to a limited extent for small screws, the even-numbered ones being more common than the odd-numbered ones, which are mainly used in model engineering, where you get things like a 5BA screw with a 6BA hex head to model large bolts without the head looking too big.

BSW (British Standard Whitworth) and BSF (British Standard Fine) are dead for new work, and difficult to get feplacements.  there are a few odd uses; camera tripod screws are 1/4" or 3/8" Whitworth for example.

UNC and UNF (Unified course and fine) threads are also pretty much obsolete.  They were imperial sizes, but with a 60 degree thread form, as used with metric threads, rather than the 55 degree used with Whitworth.

BSP (British Sandard Pipe) is still used; there was a special thread with a finer titch for thin-walled electrical conduit, but I think that's been replaced by a metric one now.

There was a special one used on bicycles for some reason.  Then there are special very fine threads for things like optical fittings.

Gas cylinders still use Whitworth threads , at least the ones that have threaded fittings, most butane cyclinders now have clip-on fittings.  I remember cutting threads for propane fittings, 5/8 BSP left hand I think they were on a metric lathe, and had to set up a strange gear train, with a 127 tooth wheel I think it was, to cut this with a metric lead screw.

Just about everything else is standard metric threads these days, identified by a letter 'M' followed by the diameter and the pitch, both in milimetres, e.g. M10x1.25  Metrication makes everything much easier; I'm from the last generation that started out learning in the old units, we used them in primary school, but by the early years of secondary school, age 11 onwards, metric was gradually introduced.  The conversion is just about complete now, Beer is still sold in pints unless it comes in cans or bottles, Milk is in pints if bottled but in litres if in cartons, carbons for arc lamps were interesting; for a far back as I can rember the diameter was in milimetres, but the length was in inches, e.g. 7mmx8" negative and 8mmx12" positive.