Double-bolt unit including slip disk and application thereof

A punching tool in a press die set, the punching tool comprising:

• a punch to create a hole in a work piece by punching action;
• and
• a double-bolt unit coupled to the punch;
• wherein the double-bolt unit comprises:
• a first bolt;
• a second bolt;
• and
• a slip disk having substantially a disk shape, the slip disk placed on top of the first bolt and below the second bolt and concentrically with the first bolt and the second bolt around a cylindrical axis, the slip disk being configured to contact a portion of the first bolt and a portion of the second bolt, wherein a first radius from the cylindrical axis to the portion of the first bolt in contact with the slip disk is configured to be larger than a second radius from the cylindrical axis to the portion of the second bolt in contact with the slip disk to have a first torque related to the first radius for turning the slip disk with the first bolt is larger than a second torque related to the second radius for turning the slip disk with the second bolt,
• wherein
• when the first bolt is positioned at a predetermined position and the second bolt is turned, the second bolt slips on the slip disk while the slip disk is fixed stably on the first bolt, according to a difference between the first torque and the second torque, thereby preventing lowering of the first bolt below the predetermined position.