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O-Ring Size For Bison Tubes


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I wanted to get some spare O-Rings to replace the missing ones on the Bison's I keep finding with the seals missing. I wasn't sure what size to get. I have an assortment kit (of fractional sizes) but nothing seemed to be a perfect match and there were only a few of each size.


Keep in mind this is for what I would call a 'standard' Bison tube. The bison's I have measure 14mm (or about 9/16") outside diameter. I ordered a pack of 50 Viton (good stuff) O-rings from eBay for about $6 and they are a great fit. What I ordered was 11mm inside diameter with a 1mm cross section. If you see metric O-rings listed as 2mm cross section, they are a bit too fat and probably aren't metric anyway, they are probably 1/16 inch.


Hope this saves someone some research.

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Jester - There are number sizes for O-rings, and from my limited understanding a #13, which is really a -013 would be a pretty close fit for a normal bison at 7/16" but a bit fat in cross-section. You can see a boring size chart here: http://www.marcorubber.com/sizingchart.htm These are non-metric sized O-rings, but of course there is a lot of overlap.


Your #6, if it translates to a -006 would be really small, so maybe you are right in thinking you are dealing with a manufacturer's proprietary sizing.


I figured most Bisons are made overseas and would be metric. But in the case of geocaching if you get a size that's close and it seals, it's good enough. If you were working on the Space Station things would be more critical.


I got a bunch of the 11mm x 1mm size so a buddy and I can replace the O-rings on a few of our own caches (I mostly hide bigger stuff) and to replace missing O-rings on others as we come across them. This is assuming the log is dry, otherwise there's no point.

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