The Chuck & Key 1.0 - 19.0 JT4 Taper Mount is a tool designed for securing and holding workpieces in place during machining operations, such as drilling, milling, or turning. The "1.0 - 19.0" refers to the range of chuck sizes, indicating that the chuck can accommodate workpieces within this size range (1.0mm to 19.0mm). The JT4 taper mount ensures a precise fit for the chuck onto the machine spindle, providing a secure and stable hold. The key is used to tighten or loosen the chuck, allowing for easy installation and removal of workpieces. This type of chuck and key setup is commonly used in lathes and drill presses with JT4 (Jacobs Taper 4) spindles.