ekstrudeeritava tooriku või külmvormpressitava toote lõpuosas, telje piirkonnas asetseva metalli defektne (oksiidne, poorne) piirkond (vt ekstrusioon), a central oxide-lined discontinuity that occasionally occurs in the last 10 to 20 % of an extruded metal bar; it is caused by the oxidized outer surface of the billet flowing around the end of billet and into the center of the bar during the final stages of extrusion (see: extrusion)