Size: 5/16"Ensure that your finished document is both fully functional and long lasting with these CombBind Binding Spines. Black, 19-hole, 5/16" plastic spines bind up to 40 sheets. Permanent spines allow pages to lay flat, helping to ensure the final product is manageable and easy to read. Durable plastic spines wont scratch, peel, chip or discolor for long-lasting use. With 125 spines per pack, you can keep plenty on hand to use for all your binding projects. For use with letter size documents. Spines are compatible with any comb-style binding machine.