The Steamboating Forum

what thread is this

I think we'll need a little more information.

It's not 1/4 npt it's on a reflex gauge valve and although looks like 1/4 npt on the boiler the plugs don't thread in like all the rest. The diameter is .490 and the threads look a little finer.

Where are you from John?

Here in New Zealand we get a mix of threads. Most are British Standard Pipe threads (BSP) and some are NPT They are similar but different. NOT interchangeable!

1/4 " BSP has 19 TPI compared to 18 for NPT. Also NPT has a thread angle of 60 deg compared with BSP of 55 deg.

Cheers

Paul

I,m in Canada, it kid of 20 tip, so it must bps. Thanks

I needed a fitting for one of my gauges [which I think were made in Wales] They turned out to be British Modelers Thread BMT Apparently when scaling down there wasn't enough threads per inch so they made their own thread design.Someone want to tell me if my tale is correct? Den

I have a set of the taps and dies. From when I was building a lot of Stuart engines and before I came to my senses and started using standard stuff.

Mike

farmerden wrote:I needed a fitting for one of my gauges [which I think were made in Wales] They turned out to be British Modelers Thread BMT Apparently when scaling down there wasn't enough threads per inch so they made their own thread design.Someone want to tell me if my tale is correct? Den

I know of nothing over here (U.K.) that is classified as British Modellers Thread (BMT), but we do have Model Engineer's Thread (M.E.) which comes in three pitches, 40 tpi, 32 tpi and 26tpi. These threads are all the smaller imperial sizes ranging from 1/8" up to 1/2" dia. There is some crossover of pitches and sizes in the commonly used ones, though I believe all pitches are quoted for all sizes. Other sizes used for fittings are B.S.P (British Standard Pipe)

Most common sizes,

1/8" x 40.
5/32" x 40
3/16" x 40
7/32 x40
1/4" x 40
1/4" x 32
9/32" x 32
5/16" x 32
3/8" x 32
7/16 x 26
1/2" x 26

The form for all these is I think 60 degs.

A good source for taps and dies generally, and these sizes in particular, in the Uk, is http://www.tracytools.com. No connection other than a very satified customer, their service is superb.

Thanks Mike At least I remembered the "model" part.Even when I was younger my memory wasn't really good