THIS IS A JACOBS 18N HEAVY DUTY BALL BEARING SUPER CHUCK, A TYPE OF TOOLING AND ACCESSORY DESIGNED FOR DRILLING. THE CHUCK FEATURES A PART NUMBER OF 18N AND IS EQUIPPED WITH A 4MT ARBOR. IT OFFERS A GRIPPING CAPACITY RANGING FROM 1/8 TO 3/4 INCHES, WHICH CORRESPONDS TO 3 TO 19 MILLIMETERS. THE TECHNICAL SPECIFICATIONS ALSO NOTE THE INCLUSION OF A CHUCK KEY, WHICH IS DESIGNATED AS SIZE K4.