The inner cavity of all toploaders are measured in the PT scale, from 20PT all the way up to 360+ PT, and determine how thick of a card can fit or should fit into the toploader. The higher the PT value, the thicker the card that should be used for that toploader.
But what is a PT and how is it measured? A PT is a unit of measure that means 1/1000 of an inch and it measures the opening width of the toploader. For example a 35PT toploader has a 35/1000" opening at the top and 100PT toploader has a 100/1000" or 1/10" of an inch opening at the top to insert cards.
To validate the size of your toploaders you can use a micrometer and measure the internal cavity. This will be difficult on the smaller 35PT toploaders but we provided an example of this for a 130PT toploader in the picture. You can see it measures 0.13 inches or 130/1000 inches or 130PT!