Used. The CAT40 Tool Holder Tightening Fixture is a tool holding accessory designed to securely tighten CAT40 tool holders. This fixture provides a convenient and efficient way to tighten the tool holders, ensuring they are properly secured for use in CNC machining applications. It is a valuable tool for maintaining precision and accuracy in machining operations, and it is commonly used in industrial settings where CAT40 tool holders are utilized.