On Tuesday, January 22, 2019 at 11:48:01 AM UTC-5, OHM Ω http://aviation.derosaweb.net wrote:
Gary,

I assume by largest you mean diameter, not length. I am also assuming that you want to find/buy an O2 bottle to fit an ASW-27. You know what they say about assuming.

After I bought my ASW-27 I had to do some major league searching to find a bottle that would fit my ship. Took more than a year to find one. Luckily a friend that owns an ASW-24 lent me his bottle for a western trip. Thanks, Geoff.

Bottom line is that the critical dimension is the diameter (no duh) which, to me, is rather difficult to measure accurately unless you have a particularly large caliper hanging around. Accurate measuring is especially dicey when you are asking a seller of unknown resources/capabilities to measure their bottle.

So, using my friend's bottle, I came up with the following CIRCUMFERENCE which is much easier to measure accurately. This I could then give to prospective bottle providers for them to measure what they have in stock before purchasing.

Here is what I came up with;

Circumference = 13-5/32" = 13.15625" = 334.2mm
QED Diameter = 4-3/16" = 4.1875 = 106.4mm

So, how to have someone else easily accurately measure circumference? A carpenter's steel measuring tape will NOT wrap around a cylinder. A tailor's cloth tape is great but is much less likely have be available. The easiest way I found is to have the seller wrap a (long narrow) piece of paper around the bottle, mark where the edges meet, lay the paper out flat on a table, and then accurately measure between the marks with a simple flat ruler (preferably in metric as +/- 1mm is ok but counting 16ths of a inch is more prone to error - ask me how I know).

Be prepared to suffer multiple disappointments in your search.

My overblown $0.02,
John OHM Ω

PS - Asking the ASW-27 Yahoo group may dredge up something for you. https://groups.yahoo.com/neo/groups/ASW27owners
Or post to http://glidersource.com which is where I ultimately found my bottle.

Hi John,

the suggested paper-strip method is a very good fix to get the dimension one is looking for quickly and probably with sufficient accuracy. If more precision is needed, a π-tape comes in handy:
https://www.newmantools.com/pi.htm
Comes in metric and for I.D. and O.D. measurements. Not sure how much they charge for one, though. Good to have a buddy in the metrology lab .... ;-)

Uli
'AS'