Tube piercing is different from traditional hole punching in that a die is not employed on the underside of the material. Instead, external guides encapsulate the tube to maintain consistency in its outside dimensions. Once the guides are fully engaged around the tubing, a punch that runs through the ID of the top guide is pressed into the wall of the tube. Thus, before punch breakthrough is achieved, the material is stretched as far as its elasticity allows, producing a dimple around the hole.