Mystery thread pitch on waterglass drain stem

[Steamin]

I'm still overhauling this 1" scale LE Pacific, cleaning-repairing-replacing as I go through it. I'm inching closer to putting the boiler back on the chassis which is now assembled, clean and shiny.

Turning my attention to the waterglass, I get all the valves unstuck, taken apart and cleaned. The last valve, the drain, is missing the handwheel nut, so it only unscrews from the stem and does not open the valve.

Measuring the diameter across the threads, I mic 0.072 inches. This is pretty close to a #1 screw size, so I rummage around and find a #1-72 in the drawer. I chuck up some hex brass stock and make a couple nuts. They won't go 1/2 a turn onto the stem. Well, I think, 72 is a fine thread, maybe the stem is a course. I close my eyes to the price and order a #1-64. When it arrives I make a couple more nuts and get ready to move on. Except the 1-64 nuts only go 1 turn onto the stem. ??What kind of special thread is this?

I don't have a print for this appliance, so I am guessing the original builder purchased it machined somewhere around 1975.

So to the board: Let me know if you recognize the waterglass below and what thread size the stems are. The Upper and Lower valve assemblies are a casting, which the drain stem is in. I still need a nut for this stem!
Steamin

WaterGlass Assembly with drain stem missing the nut. also a victim of the upside down photo orientation.

[Builder01]

Might be a BA thread.

[Bill Shields]

Even though a LE loco...the British have been selling a lot of fittings for best part of a century. Impossible to tell from a photo since these things changed outward appearance on a regular basis.

BA as suggested would be my bet..

Which would mean that all the other small threads could be BA as well....be careful or you may need to replace the entire assembly which may be cheaper than an assortment of taps and dies from the UK.

[jtdute]

That is an old Tru-Scale water gauge. By my notes and drawings the thread is #1-72. Those threads where cut with Geometric die head so the OD of the threads may have been off.

Jeff

[Builder01]

A jeweler's loupe and a thread pitch gauge would help a lot. If you don't have either, maybe it's time. If it is BA, it won't match up with "threads per inch".

[gwrdriver]

That is an old Tru-Scale water gauge.

Made for and sold by Coles Power Models. I have one exactly like it.

[SteveR]

Is the tube that the gauge mounted on a water column? Why do some folks use them and some not? Thanks for noting that the picture is upside down!

SteveR

[Mike Walsh]

Worst comes to worse, make up a new valve stem!

[Steve Goodbody]

Hi Steamin,

For BA, 0.072" OD would suggest 9BA which is a very unusual size. The most commonly-used BA sizes are the even numbers, FYI.

That said, I have a full set of BA taps and dies, and many BA nuts and screws. f you were prepared to send me the spindle and/or handwheel, I could probably help you out with something if it's indeed BA. PM me if that's of interest.

Best regards
Steve

[Steamin]

Happy the learn the name of this waterglass - Tru-Scale.

If it is a BA thread I would probably make a new one instead of trying to match existing. Up to now I have been avoiding making a new valve stem because I don't have another handle, did not want to have one stem with different threads than the others, and, lacking a die, would have to make a single-point tool which will thread to a shoulder in the lathe.

I do have a jeweler's loupe and other magnifying devices to help my poor vision but my thread gages only go to 40. Might be time to get a microscope, I am having a hard time seeing the thread fit using the taps as gages.

@SteveR; Yes, the glass tube is mounted on a water column. Usage of a water column can mitigate problems with steam bubbles showing up in the glass and bouncing/fluctuating water level caused by the boiling action. It is builders preference whether one is used or not. For some, the placement of the fittings on the boiler give no waterglass issue and a direct mount is used, for others their boilers give bubble/bounce troubles which the water tube can mitigate.

[jtdute]

I (LocoParts) have those hand wheel castings available.

Jeff

[Mike Walsh]

I have a water column at home. I doubt it is the same, but it came off of a Pacific. I will check to see if it is the same. If so, I will verify that it has all fittings - you can have it if it is the same.