It's frustrating buying top loaders online, thinking you purchased the right ones only to have them not fit your card perfectly.  We want to help you get the right ones the first time. 

Most top loaders are measured by a point scale.  This is the size of the opening of the top loaders.  The higher the number, the larger the opening. 

Here is the best way to figure out how thick of a holder you need for a given card.  Take a stack of common cards and lay them on top of each other. 

1 regular card = 20 Point - Use all standard Top Loaders or screw downs.
3 regular cards = 55 Point - Use 55 point Holders or 1.5mm (we currently stock both Cardboard Gold and Ultra Pro brands for this size).
4-5 regular cards = 70-75 Point - Use 75 point Holders or 2.5mm (we currently stock both Cardboard Gold and Ultra Pro brands for this size)
6 regular cards = 100 Point - We carry the Ultra Pro 100pt top loaders and magnetic one touch holders in this size.
7-8 regular cards = 138 Point - Use 138 Point Holders or 3.5mm (we currently stock both BCW and Ultra Pro brands for this size)
9-12 regular cards = 180 Point - Use the 180 Point Holders or 5mm (we currently stock Cardboard Gold brand for this size)

Hope this helps you choose the right holder for your cards.  As always, we are here to answer any questions.  Just fire us an e-mail at sales @ columbiasportscard.com