There always comes a time when we are working away and "WHAM we are stopped in our tracks because an "O" ring breaks, splits or just goes away. The industry can't make specific "O" rings for everything so they've standardized the sizes to a modest 50 or so for us reloaders uses.
Kenetic bollit pullers are the SAME SIZES internally, and parts are basically interchangable for them.
I only use the Lyman boolit sizers, #45's and I've used some #450's and they use the same "O" rings also.
Here is what I've been using for decades, and they are all available from Home Depot, are under the brand name "Danco" come in a pack of 10 each, and cost (at least here in Florida) $2.69/pack of 10.
The little "O" ring that holds that infernal top 3 piece assembly together in your knetic boolit puller is a #35 item #96749
The Lyman presses use two "O" rings and they are:
Small - #35 item #96749
Large - #15 item #96732
So with this information, you don't have to go ordering from the manufacturer any more, just go to Home Depot and for under $6.00 you should have almost a life time supply of "O" rings now.