Question about O-rings

[SkinWalk3r]

I want to stock up on O-rings. Which ones are most likely to wear out.
I want to be able to buy them on eBay so could someone tell me which types as in model types to get please.

[chnk]

regualr tank orings are fine, you honestly don't need that many,

i've bought a 1000 orings for $5 and i've gone threw 20 the most,

polyurethane rings seal better than regualr tank orings but they do cost more and same goes for x rongs. yo might want to get some of the red striker orings also