apparatus and method for assembling a pair of thin - walled metal container counterparts which are brought together axially , are rounded and one inserted into the other substantially without deformation of either of the pair of counterparts so that the inner part is allowed to expand , after insertion , radially and both parts at their juncture are stressed in hoop tension for tightly embracing an adhesive interposed therebetween and thereby insure a good bond at the seam .