Model pipe threads?

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Model pipe threads?

Post by DianneB » Thu Oct 05, 2017 7:41 am

I have an assortment of live steam fittings made by others and a few taps and dies I have accumulated but I find ti very difficult to identify the types of threads. Diameter and pitch are easy to measure but taper is more of a guess. Once I have diameter and pitch, I usually still don't know what thread it is.

Does anybody have a link to thread details for all the various common "live steam model threads"? There are SO MANY and I haven't been able to track them all down :(

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Re: Model pipe threads?

Post by RET » Thu Oct 05, 2017 8:38 am

Hi Dianne,

There are two Model Engineer thread series, 32 tpi. and 40 tpi. in fractional sizes from 1/8" up to 1/2". Taps & dies are available for both series, probably from England. The 40 tpi series is not so common and is mainly used for threading tubing. These are parallel, not taper threads.

In addition, there is the B.A. series (British Association), which goes from 0 to 14. 0 is the biggest, while the tap drill for #14 is 3/4 of a millimetre.

While i have some ME taps & dies, in my model work, I often use National Fine taps because I have a complete set of both NF and NC and the National Fine is a good compromise, giving strong threads that don't look too out of place in a model. When you get a model made by someone else, it can often be quite difficult to find out what threads were used.

I keep my different taps (and in some cases dies) in wooden blocks with the different sizes left to right with the taper plug & bottoming taps for each size one behind the other. This way I have fast & easy access to the tap I want. I often use a tap as a thread gauge, but that doesn't always work. In addition, I have a set of BSF and BSB taps & dies which I almost never use.

I never use taper threads in my work; I like to use National Fine with "O" rings for sealing against the flat face of the boiler bushings for instance. The "O" rings give leak free connections that don't leak and are easily taken apart.

Hope this helps a bit.

Richard Trounce.

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Re: Model pipe threads?

Post by NP317 » Thu Oct 05, 2017 8:51 am

PM Research has a coherent description of threads commonly used on our models:


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