Abstract: The instant invention relates to a device for testing the end buckling strength of a can body wherein a uniquely disposed compressible ring- or doughnut-like member of appropriate elastic material is adapted to be compressed against the inside surface of a metal or container for the purpose of sealing the interior of the metal can from the atmosphere. The sealed interior of the can is then subjected to appropriate fluid or air pressure to determine the buckling characteristics of the can's closed end structure, after which the can body can be released from the testing device in an improved fashion.