On Jun 12, 11:46*pm, Ned Simmons wrote:
On Sat, 12 Jun 2010 18:13:36 -0700 (PDT), Vernon Tuck

wrote:

I'm not a machinist and I don't have any measuring tools. *So I'm not
sure about the diameter of these holes but I'm pretty sure they're
M20x1.5 or M21x1.5. *I have found European sources for blind plugs in
these dimensions but have not yet found a source in the USA.

These seem to be intended for use as conduit fittings, but the threads
are right:http://www.sealconusa.com/strainreli...m/adapters.htm

McMaster has some as well, but a quick look showed only very expensive
high pressure SS fittings there.

4822T45
Extreme-Pressure SS Threaded Fitting M20 X 1.5 Male X 1/2" NPT Female
Adapter, 5000 PSI
In stock at $46.63 Each

--
Ned Simmons

I found the M20-1.5 drain plug in an auto parts store. They were kind
enough to let me try it on the tank. It was too small. They also had
a drain plug in M22-1.5. I now know that is the correct diameter and
thread pitch. However, the shape and mass of that drain plug were
unsuitable. At $12 a pop (and I need 3 of 'em) it turned out to be
too expensive, also.

After going back to google again and again I think I have correctly
surmised that PRESSURE WASHER HOSE FITTINGS will work. They're the
right diameter but I'm not sure they're the right thread although from
the picture it looks about right. So I bought 3 fittings for $3.00
each. Not only are they pressure rated they're also made of brass.
That strikes me as a good thing so they won't get frozen by rust
developing between the fitting and the tank.

The fittings I ordered are both male, 22mm at one end and 3/8" at the
other. I am hopeful, but probably delusional, that the smaller thread
will fit a standard air hose quick disconnect.

I have learned that 22mm bolts, when available, are ridiculously
expensive. So if these fittings don't work I will probably launch the
tank into near earth orbit.

Thanks,

V