I bought some packs of 12, 13, and 14 mm OD O-rings on Amazon for my Tobeco Kayfun 5 clones - but they seem a fair bit “stiffer” than the ones in the Tobecos.
That property (in the Buna-N composition O-rings that I think are used on RTAs) is called the “Durometer”.
Has anybody determined the “Durometer” of O-rings in their RTAs ? They might well be similar to mine.
Here is a more in-depth rundown:
The durometer has a calibrated spring which forces an indent or point into the test specimen against the resistance of the rubber. The indicating scale reads the hardness of the rubber. If there is no penetration, the scale will read 100, as on a flat glass or steel surface. … For most applications, compounds having a Shore A durometer hardness of 70 to 80 is the most suitable compromise. This is particularly true of dynamic applications where 90 durometer or harder compounds often allow a few drops of fluid to pass with each cycle, and 50 durometer compounds tend to abrade, wear, and extrude very quickly.
In addition to my Kayfun 5s, I have an eXpromizer V3 on the way (which very likely uses some different sizes in the critical locations to maintain) - so I am looking at O-rings (Duro 70 and Duro 90 are said to be the most often used, but I don’t know if they are appropriate).
Not clear whether this company (referenced in Dan’s post above) will sell directly to individuals for single small orders - but here are selections of their Buna-N Duro 70 and Duo 90 kits of selections of sizes:
Any known good sources (ideally that sell small lots in specific sizes, rather than a kit full of misses) ?
From a reference on the one other related thread that I can find here, it look like this company might allow one to acquire small lots of specific Duro 70 and Duro 90 O-rings. Curious as to the “70 or 90” question.
I find but one lone mention (of a desirable “Duro” rating) from one ECF poster in 2011 (“Shore A” is the common scale): I would go with the Viton® Fluoroelastomer type with a Shore A: 60 Medium Hardness …
Update: So I am (hoping) that Duro 70 rating will be more like the O-rings to be replaced, and for $2.50 + $3.00 Shipping (ie), a total of 250 12, 13, and 14 mm OD O-rings for $5.50. Nice ! One penny each + ship. Or, consider “living it up” with “Viton” Flourinated High Temp Resist (Duro 75) 12, 13, or 14 mm OD O-rings.