Model Engineering Threads

Can I ask why and when are ME threads used please?

Are they a scaled down version of BSP threads?

Thanks Guy

Hi Guy,

The ME threads have 32 or 40 TPI Whitworth form and the same TPI for many different diameters, and I have only seen them on boiler fittings. For the BSP threads the number of threads per inch varies with the diameter.

Thor

You can use them anywhere that you need a fine thread, often boiler fittings but also good for needle valves or tooling as 40tpi gives 0.025" per rev like a micrometer.

Fine metric threads tend to be used for similar things in the rest of Europe and I also use 0.5, 0.75 and 1.0mm pitch metric threads more and more as I am making more metric models.

BSP, G in Europe or NPT if in the US can also be used for steam, gas and water fittings on larger models for example the hit and miss engines I make often have BSP threads for the exhaust and water cooling pipework.

5/16" x 32 is effectively interchangeable with the standard tyre valve thread, and enables the convenient use of tyre inflators to run stationary engines.

The ME thread is the old Whitworth extra fine thread, In USA there is an equivalent in the UNEF. These threads are ideal when fine adjustment is wanted. On models it makes a nice scale thread in places where even BSF looks too course.

Ian S C

They fulfill a number of needs:

An alternative to BA sizes for small threads that use standard stock sizes.

• Fine pitch so ideal for assemblies where there isn't a great depth of metal to take the thread.
• Two constant thread pitches, sometimes useful for sadjusters etc. Also makes machine cutting more straightforward.
• Often look good on models.
• All use the same (Whitworth) thread profile.
• Many sizes overlap with other thread series so most taps and dies didn't need to be specially made.

40 tpi gives 0.025 inch a turn so good for micrometer type adjusting dials .

1/4x 32 is used on small spark plugs and glow plugs . Other than that it is not really common , BA is mor common .

Spark plugs and glow plugs are 14 x 32 UNEF 60deg not ME which is 55deg though you may get away with mixing the two.

I suspect the same happens with 26tpi, as I have seen a number of sets of taps and dies sold as Cycle Thread/British Standard Brass, despite the difference in angle.

in addition to 26, 32 and 40, there appears to be another whitform series at 60tpi, referred to by C. A. Amesbury in a 1973 Model Engineer, and still available from Tracy Tools (who fittingly list 26 diameters of BSB). Are there any other series?

Brian

EDIT:  Which is worse, a motorcycle chassis with mismatched threads or a safety valve?

Edited By Brian G on 09/10/2018 14:30:54

I think that should probably be C. R. (Roy) Amesbury but apart from that LBSC mentioned 1/8" x 60 ME Taps & Dies as being available in the early 1930's in an article about building a Weir Pump.

Apologies for the error, having tracked down (alright, searched on eBay) those back numbers specifically for his article, I should have got his name right.

Re-reading the article he describes making his own taps and dies because "I don't suppose any of these can be purchased these days and I doubt if there is a metric equivalent!". Sometimes we forget just how much easier the internet can make sourcing this sort of thing. Had my 14-year-old self wanted to buy an unusual tap in 1973 it would have meant writing many letters (enclosing the usual S.A.E.) and waiting for replies, or an equal number of calls from the phone box on the corner.

Brian

Thanks for clearing that one up for me chaps

Best

Guy