What's the pitch of the thread on a Smith speedo housing ?

email (option): viaconsu # planet dot nl

Hi Hans,

Please go to my web site www.britishtool.com and head for the thread section (taps & dies etc..)

I have charts of all tbe British threads on a bike or car. You are free to download them and use them as you will.

The threads on all instruments are usually BA (British Association).

Cheers

email (option): britool51@hotmail.com

Thanks Robb, I already have them!
But my problem is that the thread is a bit knackered and it is difficult to measure the pitch because it is very narrow. It is something like 26 or 28 tpi. And before I try to put the bezel on, I would like to know what thread file to use to fresh up the thread!

email (option): viaconsu # planet dot nl

Hans, do you mean the bezel thread? There have been suggestions that due to the original licensing agreement with the French Jaeger company, British Jaeger and then Smiths in turn were compelled to retain the metric threading.

The studs underneath could indeed be M6 rather than 0BA which are effectively interchangeable but I've never had to investigate the bezel threads. Can you find a metric pitch that fits ?

Hans, if you measure the spread and the # of threads in that small space, on the bezel, you should come up closer to 26 and I was using the Whitworth 55 scale.


Take that thread gauge and run it though the edge, it cleans my gunk very well at 26, the teeth are deeper

email (option): unpob@yahoo.com

The BA thread form was originally based on Swiss Clock threads and is in fact a metric thread form, being based on the meter and with metric pitches and diameters. Included angle is 47.5 degrees. The speedo case (bezel) thread is most likely 0 BA..which is 25.4 threads to the inch..or a 1`mm pitch if you prefer. The BSI recommended the replacement of 0BA when used for studs with 7/32 BSF..so that is another possibility for the mounting studs..though that has a pitch of 28 TPI so some careful checking will be required. I think 0BA is more likely on the Smiths speedo. A 6mm thread shares the pitch of 0BA at 1mm but the included angle is bigger at 60 degrees and the radii at the base and crest of the thread differ so they are not really compatible...just similar...Ian

email (option): ian@wright52.plus.com

As a matter of interest has anyone worked out what thread it is where the speedo cable screws on?....Ian

email (option): ian@wright52.plus.com

Hi Ian, 26 still looks good, but I think the expert on this is JJ cables!

email (option): unpob@yahoo.com