hey vernon,
well you're wondering about the sizes versus they type material in these other kits you have as to what is actually in the machine your fixing to tear down?
Addressing this i can say most orings are either rubber or neoprene and generally they use standard black rubber or neoprene in these applications. The only time you will see different ones are in cases where there are special chemical exposure or heat related instances where the orings will be colored green or red or tan colored.
The sizes depend on how the engineering guru's designed it, there is no industry standard across all machines built across the spectrum of mfg's, at least none that i've seen in any regular fashion.
One possible way to find out is to go to bigjoe's website and look up the parts and see if they were kind enough to list the sizes in the part description, sometimes they do. If there are 'kits' they generally don't. You can call them directly and give them the model and serial number of the machine your working on and tell them what component your wanting to reseal and they 'might' be able to tell you the sizes but that is a coin toss because they might not be willing to tell you that much detail due to proprietary copyrights that they just don't want you to know. Yeah it does sound trivial but these mfg's are strange like that so you just have to deal with it if they are not willing to tell you.
Can you give me a specific model and serial number of your machine? and be specific on what your wanting to rebuild/reseal? Then i can tell you if there are any surprises you might be looking at that could be considered unsafe or require special tools.
Without knowing exactly what you're working on i'm just guessing here ;o)

I just checked and as far as bigjoe and liftrite they are not the same company, liftrite has it's own website and bigjoe has their own, they do not appear to be affiliated. So you either have one or the other, they are not of the same mfg.

Maybe I should have been more specific. I should have added (or just asked in the first place), does anyone know what sizes generally come in the seal kits. I'm going to bust it open sometime within the next few weeks. Also, any surprises i should know about. Like....packed ball bearings that like to fall oit all at once loaded springs that fly 20 feet or 4 feet and wont know till i step on it 6 months from now. Or needle size pins that i totally will miss and wonder why theres hydraulic fuel leaking everywhere two hours after rebuild. I'll be popping my "liftcherry" and though I never let fear or common sense get in the way. I dont want to end up wasting my time doing it three times. There are some utube vids but not as specific as i think I'm looking for. @swoop223 thanks for the help m8.....eh!!

well of course they want you to buy their parts to insure you get the right parts to put back in the machine. ;o)

on that note i will say this,
o-rings come in all types of compositions so if the o-rings you have are the same size and type material as the ones in the jack then i cannot see why you couldn't use them.

BTW... a pallet jack is considered part of the material handling world so why not post here? a pallet jack has forks and it lifts so why not eh? ;o)