If you are ordering a bidet, you can add an extra O-Ring for $0.25. If you are returning after having ordered a bidet and only need an O-Ring because you want your bidet to fit a different bottle, check the ship-one-O-Ring option and it will run you $1.
 
And now this description starts getting long. After posting this a couple weeks ago I see a trend building.
 
1-People just buying extra O-rings for whatever bidet they are buying. These are strong O-rings, they are not hardware store or even box box store O-rings. No one has just broken an O-ring except my mom who somehow p[erfectly cut into one with her nail while putting it on. I have O-rings out in the yard on test bidets that have been there for years and they are still perfect. If you need one to feel psychologically safe go for it!
 
2-People just buying one of everything. Here goes the compatibility:
The O-ring on the standard bidet fits the Mazuma bottle perfect, and the CNOC thrubottle a bit tight as described in the thrubottle description.
The NOBO )-ring fits only the NOBO bottle.
The CNOC oring fits only the 28mm soft flask CNOC products. 28mmis the smaller of the two openings CNOC offers.
 
Everything below is optional reading.
 
Why won't I give out the size?
People write in asking for the O-Ring dimensions so they can grab one at the hardware store. Store-bought O-Rings crack after about a year. Not a guess. That is where I started, and I left mine outside year-round to push the experiment.
 
You can also source the exact same size and the bidet still will not work. Not always true for the NOBO or CNOC bottles, but for the standard bottle O-Ring it is very true. The O-Ring I use comes from one factory in the Philippines and something about how it is made produces just the right amount of friction. Nobody at the company I order from can explain it. Once they filled my order from a different factory, same exact size, and they did not work. I keep a three-year supply in my basement now out of fear some President might come in and mess with international trade :)
 
They are also food-grade. Non-toxic, chemically resistant, safe for direct food contact.
Strong too, with one exception. My mom mentioned the CNOC O-Rings were breaking on her occasionally. I tried to snap one myself and could not do it. It turned out it was her nails. One small nick and the O-Ring will snap when you stretch it on.
 
Why does one O-Ring cost a dollar?
Getting it to you cost:
$0.80 stamp
$0.10-$0.28 per O-Ring
$0.08 Envelope
 
R&D Cost:
$40ish buying bottles to test compatibility
$Unknown, time driving to hardware stores
$Unknown, time spent standing in the dark corners of the hardware store testing for correct size
$Unknown, time spent finding a place that sells the exact size made of the material that meets Holey Hiker Bidet standards
$5 paying my local hardware guy for a single O-Ring because I appreciate him being there
$Unknown, extra fiber on day one so I could go on day two and test the orings
 
One dollar is a pretty good deal.