With some of our files you can choose between 2 & 4 ring mechanisms and also different capacities of mechanisms. The latter is the internal space allocated to accommodate all your documents / paper sheets. On some products our capacity options range from 15mm Slim to 55mm Lever Arch mechanism. On each product page we give you an indication as to how many sheets the given capacity you have selected will accomodate, although this is dependant on the grammage (thickness) of paper you have and whether you are using plastic sleeves for your documents.