I mean an old one of course.

Bazyle is probably correct old Meccano screws are 5/32 Whitworth 0.1563 x 32 tpi.

It is highly doubtful that Bridges would have used metric screws back in the day.

Could it be 2BA ?

edit: oops no, wrong diameter.

Ed.

Edited By Ed Duffner on 18/04/2016 19:47:56

bsc 32tpi 3/16th 0.0312 pitch?

I've got a scrap Bridges drill here. Do you want it for the fasteners. Easiest if I strip it and post you the debris. If interested PM me with name and address and I'll get my Black and Decker electric screwdriver on charge…

Rgds Simon

The mixture of thread types reminded me of an amusing story way back when I first joined my last company.

The company manufactured military radios for the local defense force and as such had a resident GI (government inspector) who floated between the various companies to attend to signing off the acceptance documents for finished goods. Apparently he had been told to ensure that we and the other companies stuck to the letter of the law regarding legislation. Now this country had accepted that metric was the way to go many years ago and hence all fasteners had to be metric, despite the many advantages of other thread types for some applications.

We many years ago bought the rights to manufacture a man-pack radio from a Danish company and this used only BA fasteners, don't ask how they chose these, but we had extensive stocks of BA screws and all the castings were tapped in house with BA threads.

Seems the GI picked up on this and dug his heels in and refused to sign off the latest batch for delivery. This was despite the fact that he had happily signed off thousands of these radios in previous production runs. A case of covering his backside!

I had recently joined the company and got to hear of the wailing and wringing of hands over this debacle and questions were asked in lofty places as to how this cock-up had occurred. Not a problem I said, I will sort this silly bugger out!

I presented the GI with a historical document of the BA thread system, he was unaware of its history, but once he had digested the document he signed off the production without any further questions. Apparently the BA thread system was based on a Swiss thread system and it is a pure metric system, but when introduced in 1884 nobody in England trusted the French or their funny metrication ideas, so the metric dimensions were converted into imperial and everyone was happy!

Another happy side to the tale is many years later when the production of these older radios was discontinued the stores had many thousand BA screws of different sizes which no longer were required. Around the same time we got a new MD and he was a amateur clock maker and had a ML7 so I asked him if the company would consider selling the BA screws to me rather than dump them. He agreed and we bought the whole stock between us. I now have enough BA screws to last a lifetime and he has the rest!

Yes John,

The whole story of threads being metric or imperial is quite an interesting story.

In radio frequency coaxial connectors used by all and sundry around the world, there is only one true metric type. It is the APC-3.5 series. All the others are imperial threads. This caused a serious problem a few years ago when the Brussels Parliament decreed that only metric threads would be allowed. NATO finally got involved and told the EU to stuff off as they were not going to change all the rf connectors on military equipment, estimated to cost billions of USD, even if there were equivalent metric types, which there were not. The whole thing fizzled out eventually and Brussels went away with its tail between its legs!

If you wish to look at cock-eyed measurement systems, look no further than car tyres. It uses three different systems to define a tyre size. The tread width is given in millimetres, the aspect ratio is a percentage of the tread width and the rim size is given in inches. Oi Vay!

I once had an ancient Morris on which the bolts were metric thread but with imperial heads – from memory anyway. I am sure someone will correct me if I am wrong, but if I'm right, well, what a crazy system……

Since Bridges is/was an American manufacturer, I would put my money on 8 x 32 UNC.

MANY years ago, pre WW2, Morris used Hotchkiss engines, so they were metric.

The BMC A series engine rocker adjustment screws were 1/8 BSP, when the rest of the car used Unified threads. The earlier side valve engined Morris Minors, used 7/16 BSF wheel bolts. The BMC powered ones were Unified. The handbook made a point of the identification marks.

Pre WW2, C.A.V. started by making Bosch Fuel Injection Equipment, under licence, so metric dimensions were the standard. In the 50s, they bought the licence from Hartford Machine Screw to make the Roosa Master pump as the DPA, (Distributor Pump A) all drawings had to be Metric, but still use Unified threads. So the American Imperial dimensions became odd Metric ones, (1/4 inch became 6.354mm , and so on). BUT, the threads for the Injection Pipes were, like all others, Metric, (often a 14mm  fine thread).

Certain Bristol buses were powered by Gardner engines which were resolutely Imperial, BSF and BSW.

The Bell Housing was retained by 9 off 3/8 BSF bolts and three 3/8 UNF studs.  The Clutch went one better, 12 off 3/8 BSF bolts, to hold it to the Flywheel, but with 5/8 A/F heads!

Leyland drew a line, and all new designs changed to Unified threads, but the engines, gearboxes, and certain other parts were earlier designs, carried over onto the new chassis. So a fitter needed two toolkits to be certain.  Then came the 500 Series engine which was Metric, imagine the confusion when working on the "Unified" chassis, powered by the "Metric" engine, and containing original Whit standard components!

Until recently, engines which had their roots in Imperial sizes were made to Metric drawings, (so few round figures there!) but on engines which changed to use metric fasteners in most places, certain critical threads remained Imperial, because of the massive cost of converting the tightening tooling to suit Metric fasteners. It was only when the new Designs evolved into totally metric ones, requiring new jigs, fixtures and tooling that they became truly Metric.

Remember, that the Continent use threads which they call "Gas", which are actually British Standard Pipe; Whit form threads and all!

My lathe uses metric threads everywhere, except on the Mandrel, that is 2.25 inch x 8 tpi Whit form.

My Mill/Drill with Imperial leadscrews, has a mixture of Metric and Whitworth threads; the latter for the more important ones, funnily enough!

Standardisation, where art thou?

Howard

Edited By Howard Lewis on 20/04/2016 20:30:59

Edited By Howard Lewis on 20/04/2016 20:35:15