Off topic: o-ring size 3 to 8 inches.

From: Unkmar 
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I know there are a lot of DIY people on this list.
I have a project, I can create the mouth/cap to whatever size I wish.
I am looking at future availability.  What is a very common size
of o-ring between 3 to 8 inches in diameter?  My preference is
towards larger.

Please and Thank.You.
-- Lucius L. Hilley III

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From: Matt Heffelfinger 
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McMaster-Carr should have whatever size, and type of O-ring you want to use.

https://www.mcmaster.com/o-rings