I just composed a message for a member, thought I'd post it here as well while it's fresh in my clipboard, in case it might give someone some help.
Manufacturers don't make cards all the same sizes, but in general, you can follow these rules:
Most base cards will fit into regular size top loaders: Ultra Pro 3x4 Premium Topload Card Holder - 25ct Pack
Thicker base cards, such as Topps Triple Threads, Gold Standard, etc., fit nicely into 79pt top loaders: BCW 3x4 x 2mm -Thick Card Topload Holder 79pt (25ct Pack)
Single color jersey cards (not prime/patches) fit nicely into 108pt top loaders: BCW 3x4 x 2.75mm -Thick Card Topload Holder 108pt (10ct Pack)
Prime patches/jersey's (called "prime" by Panini, Topps usually calls these patches) fit nicely into 138pt top loaders: BCW 3x4 x 3.5mm -Thick Card Topload Holder 138pt -10 ct Pack
Extra thick cards, like Exquisite or Five Star, fit nicely into 197pt top loaders: BCW 3x4 x 5mm -Thick Card Topload Holder 197pt (10 ct. pack)
. (I should mention that many extra thick cards fit loosely into these 197pt top loaders - I prefer loose than too tight. If you want the tighter fit, go with these 180pt's: Ultra Pro 3x4 Super Thick Topload 180pt Card Holder - 10ct Pack
Some cards are so thick they won't even fit into the 197pt, these cards are very rare. But those you can fit into 240pt top loaders: BCW 3x4 x 7mm - Thick Card Topload Holder 240pt - 10ct Pack
Some cards are even thicker than that, booklet cards for example. What I do with booklet cards is put them into a 25 count slider box (BCW 25 Count 2 Piece Slider Box - 2ct Pack
), which will usually be a loose fit. Then I put a piece of cardboard in there with it. I keep putting pieces of cardboard until the card doesn't bounce around in the slider box, but not too tight to create too much strain. This is the hardest, but once you get used to it, it works great. You can also fold a sleeve and put that in there, if you just need a tiny more snug fit.
Remember, all the above fitting strategies have the card fitting loose-lightly snug in the top loader. The cards do NOT fit tight in top loaders. So you'll need some team bags to seal over the open end of the top loader to make sure the card doesn't slide out. (BCW Team Set Bag Resealable - 3 3/8 x 4 1/4 (100ct Pack)
) I also use Scotch Magic Tape (tabbed on one end so it's easy to peal off) to crimp the open end of the top loader closed. This way the card cannot slide out, even if the team bag opens during transit.
Hope this helps.