What O-rings do I buy?

I own 6 different pcp's and am starting to wonder what do I do when I need to replace some O-rings. Should I get 1 of these:
http://www.ebay.com/itm/SAE-Metric-Rubber-O-Ring-Washer-Assortment-Kit-Automotive-Storage-Case-ORing-Set-/112113948142?var=&hash=item1a1a8315ee:m:mBT75PrPt8oRio8LxB4N07A

or should I get these pre-packaged rifle specific rings: http://www.ebay.com/itm/FX-Wildcat-Oring-Kit/152215320741?ssPageName=STRK%3AMEBIDX%3AIT&var=451405359615&_trksid=p2055119.m1438.l2649

Any other suggestions? I don't want to go looking or ordering 1 or 2 at a time.
 
"Dirte"The metric generic o'ring kits have very little to none that fit. The specific kits will be better. If you have the o'ring sizes than order them from orings and more. A couple bucks for 50 pieces or more. A lot of the same o'rings like FX crossover to fit other FX rifles. What guns are you looking for?
FX Wildcat .25, Royale 400, Brocock Compatto .177, Vulcan Tactic .25 for now.
Thanks
 
"skohl"
"Dirte"The metric generic o'ring kits have very little to none that fit. The specific kits will be better. If you have the o'ring sizes than order them from orings and more. A couple bucks for 50 pieces or more. A lot of the same o'rings like FX crossover to fit other FX rifles. What guns are you looking for?


FX Wildcat .25, Royale 400, Brocock Compatto .177, Vulcan Tactic .25 for now.
Thanks


Another thing I may add some of those kits may be for overseas spec guns. When I ordered one for a Royale they did not include the regulator, power wheel and large valve seat o'ring. AOA sells factory kits that fit in the $40 range. I am building logs on all my guns with o'rings and parts.

http://www.fxairguns.com/wp-content/uploads/2015/10/wild-exploded-drawing-AoA.pdf

http://www.fxairguns.com/wp-content/uploads/2015/10/Royal-Drawing-and-Partlist.pdf