Chinese 8mm threads (temperature probe)

[PeeBee]

I've an Inkbird PID. I need a stainless steel probe for the PID to fit into a HLT vessel, preferably RTD (PT100) type.

Lots of probes on eBay, all from China.

First one rusted all over within days. Second one remained shiny! But the nut attaching it rusted dramatically; it certainly isn't stainless steel! Shouldn't be hard to get a replacement nut? Try M8 nut; couple of turns and binds. Buy some 5/16" (pretty close to 8mm) UNF nuts; binds within 1 turn. Buy 5/16" UNC nuts (5/16" UNC/UNF roughly brackets the M8 with differences in thread pitch); binds within 1 turn. Even try running an M8 cutter through the UNC nut to "open out" the tolerances (sort of hopeful desperation); binds!

Anyone any idea what the Chinese use when they say "8mm"? Anyone have any alternative supply of suitable probes?

Cheers

(Example of what I've been trying here https://smile.amazon.co.uk/PT100-Thread ... =8-1-fkmr1. This will be another "pretend" stainless steel probe! The Chinese really do have a good laugh at us.).

[Mashman]

When the Chinese say stainless they mean shiny, at least, for a while...

[LeeH]

1/8 BSP?


Sent from my iPhone using Tapatalk Pro

[PeeBee]

1/8 BSP?

Thanks. Haven't tried it, but 1/8bsp has 28tpi and a good bit larger than 8mm diameter (8.5 minor dia.). 5/16" UNC/UNF is 18/24tpi but both bind early. M8 is just over 20tpi and gives best fit so far, hence I think tpi is about 19-22.

[f00b4r]

It could be an American thread (NTP?).

[PeeBee]

It could be an American thread (NTP?).

Thanks. I looked it up because although it might not make sense to use a pipe thread in such a situation, it's just the sort of thing to expect from China. But in looking it up I was immediately reminded that NPT is a tapered thread. No luck there (the nut in question is a locking nut).

I think I'll have to replace the probe assembly with one sourced in Europe (which will likely be manufactured in China!). If anyone has suggestions for a source of such probes?

[f00b4r]

Angel Homebrew and Brewbuilder usually stock those type of probes.

[themadhippy]

could be imperial millimeters

[guypettigrew]

could be imperial millimeters

Not a chance. Almost certainly metric inches.

Guy

[Kev888]

Knowing chinese threads almost anything is possible, including being out of tolerance (except with each other). The only ones I had were M8 (and yes they rusted too), though they were described only as being 8mm diameter - and a foot note saying allow for 3cm error on all measurements! But there are unfortunately many legitimate options very close to 8mm diameter, with different pitch and thread forms:

1/16" National Pipe Thread (straight, not the tapered variant) has an OD of 7.95mm and a pitch of 0.94mm.
1/16" British Standard Pipe (again not the tapered version) has an OD of 7.72mm and a pitch of 0.9mm
M8 obviously has an OD of 8mm, the fine variant has a pitch of 1mm, and the standard/coarse 1.25mm
Then there are the 5/16" (7.94mm) options, UNC/BSW at 18TPI, BSF at 22TPI, and UNF at 24TPI

(Hopefully I've transcribed the values correctly, but please double-check if any seem to be relevant to you).

FWIW I ended up just using the stainless tube and discarding the threaded parts anyway, which (in my case) were not stainless in any grade that we would wish for (the tubes were just push-fitted into them). I drilled out proper stainless screws and silver-soldered the tubes into those instead, though in another case I used JB-weld rather than soldering, which also seemed to work.

[PeeBee]

Angel Homebrew and Brewbuilder usually stock those type of probes.

I must stop all this farting about; probe (1/4"BSP) ordered from Angel Homebrew (along with 14mm Q-max punch). He'll be amused, it's almost 3 years since he supplied the vessel drilled out to take these useless Chinese probes.

Thanks.

could be imperial millimeters

Would be amusing if we weren't capable of such madness over here! My favourite rant is the thread on CO2 cylinders: Described (short version) as W21.8-14 (deciphering this is a road to lunacy). Doesn't stop there, the description (long version) also includes "M22-14": The "14" wouldn't mean tpi would it? Na, can't be …

Knowing chinese threads almost anything is possible, including being out of tolerance (except with each other). The only ones I had were M8 (and yes they rusted too), though they were described only as being 8mm diameter …

Aye, I thought I had it solved when I looked at an earlier Chinese purchase (it didn't rust, the water just poured straight through it). I thought I could use the 8mm nut on it and it might be stainless steel. But the nut happened to really be M8 and would not fit to the probe I'm trying to attach.

That was enough, Angel Homebrew quickly got my order for a new probe (the fourth probe for this project!).

[Heron1952]

https://www.ebay.co.uk/itm/RTD-Pt100-Te ... 46b0b2d0f7 FWIW I use these l like being able to disconnect from the vessels.

[PeeBee]

https://www.ebay.co.uk/itm/RTD-Pt100-Te ... 46b0b2d0f7 FWIW I use these l like being able to disconnect from the vessels.

Saw them, Amazon sell 'em. But they are best screwed into a threaded pipe fitting (a thermowell?) rather than directly on to a vessel wall (the tapered NPT thread, and they are tapered in this case, makes lock nuts redundant). And I do have that type in other parts of the brewery: 1/2" male NPT will tighten into 1/2" BSP female threads, but a bit of PTFE tape is wise to fill the very slight mismatch in thread form.

NOTE: I have now purchased a 1/4" BSPP probe (extra P for parallel; tapered male BSP is BSPT). A 1/4" NPT probe will not screw into 1/4" BSP because at that size the threads-per-inch are different. There is no need for tapered female BSP threads, but for very demanding situations you can get tapered female BSP, which is confusingly designated Rc. End of public information broadcast!

[PeeBee]

…
Then there are the 5/16" (7.94mm) options, UNC/BSW at 18TPI, BSF at 22TPI, and UNF at 24TPI …

Damn, missed British Standard Fine (BSF). Too late now, but I'll record the option here should I ever want to give it another go: https://www.ebay.co.uk/itm/5-16-BSF-Nut ... 245563574 .

[Heron1952]

https://www.ebay.co.uk/itm/RTD-Pt100-Te ... 46b0b2d0f7 FWIW I use these l like being able to disconnect from the vessels.

Saw them, Amazon sell 'em. But they are best screwed into a threaded pipe fitting (a thermowell?) rather than directly on to a vessel wall (the tapered NPT thread, and they are tapered in this case, makes lock nuts redundant). And I do have that type in other parts of the brewery: 1/2" male NPT will tighten into 1/2" BSP female threads, but a bit of PTFE tape is wise to fill the very slight mismatch in thread form.

NOTE: I have now purchased a 1/4" BSPP probe (extra P for parallel; tapered male BSP is BSPT). A 1/4" NPT probe will not screw into 1/4" BSP because at that size the threads-per-inch are different. There is no need for tapered female BSP threads, but for very demanding situations you can get tapered female BSP, which is confusingly designated Rc. End of public information broadcast!

Well they can be fitted to a thermowell but they don't have to be all 4 of mine are fitted directly to the vessels, and have been for several years, without any problems.