Thread Size in Top of 15KG propane tank

[Adumbration]

Safety nannies will be all over me with this one.

 

I am engineering a special purpose air compressor.  It is an custom design to fit a specific space.

 

I will be using a 15kg propane tank as the air tank.  I have already obtained it.

 

Does anyone by chance know what thread size is in the top of the tank.  And to be clear I am not talking about the brass valve on the top of these tanks.  I am talking about the actual thread where the brass valve screws into the steel tank.

 

It is a standard right hand thread and from my measurements it is circa 25mm dia.  It looks course like BSP (not metric) but 3/4 inc is 26.44mm and 5/8 is 22.99 and neither of these measurements is dead on.  

 

Anyone know if the stated dia mm measurement for 3/4 and 5/8 above are from the bottom of the thread or from the peak.  If from the bottom then it might be 3/4.

 

Thanks for any help.  And please before all the just go to the shop and try it posts are made, please note I live in a small fishing village in the boondocks.  Any specialist parts such as this I have to buy online which is very difficult when dealing with unknown threads sizes and pitches.

[SomchaiDIY]

1/2 3/4 ngt are common size for gas bottle

[Adumbration]

6 hours ago, SomchaiDIY said:

1/2 3/4 ngt are common size for gas bottle

Not here they are not.

[SomchaiDIY]

3 hours ago, Adumbration said:

Not here they are not.

the information i give is at our scg thai gas valve ref book with ref to standard 15kg lpg tank pol valve

 

we have many industry gases valve in the factory spare stock include lpg ngt thread type

possible i have information mistake in our book for standard cooking gas tanks please tell correct size now you have correct information
 

[Crossy]

If you can't find the correct thread then simply drill and tap the fitting that came out of it to any size you like???? 

 

EDIT 3/4" NGT or NPT do seem to be the standard 

https://www.bestmaterials.com/PDF_Files/propane-fitting-threads.pdf

[Mavideol]

did you try your best friend "google" and look for thread pitch as well

 

http://www.apollointernational.in/iso-metric-thread-chart.php

 

https://www.wermac.org/bolts/bolts_thread_pitch_chart.html

 

https://www.aspenfasteners.com/content/pdf/thread_pitch.pdf

 

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[Adumbration]

19 hours ago, SomchaiDIY said:

the information i give is at our scg thai gas valve ref book with ref to standard 15kg lpg tank pol valve

 

we have many industry gases valve in the factory spare stock include lpg ngt thread type

possible i have information mistake in our book for standard cooking gas tanks please tell correct size now you have correct information
 

I might have to apologise to you.  I saw no reason why the american NPT would be used here given other gas fittings in and around regulator are bsp.  But I could well be wrong.  I will post with my findings.

[Adumbration]

2 hours ago, Crossy said:

If you can't find the correct thread then simply drill and tap the fitting that came out of it to any size you like???? 

 

EDIT 3/4" NGT or NPT do seem to be the standard 

https://www.bestmaterials.com/PDF_Files/propane-fitting-threads.pdf

That is an option but what I would probably do is buy a 3/4 stainless nipple and weld that in.  I have to weld some other connections on the tank but wanted screw something straight in to the top of the tank if I could.  I will be using the tank inverted so that the valve hole will actually be used to fit a water drain valve.  If it was not welded into place that would be better solution (corrosion wise).

[Adumbration]

This is what the hole looks like.