Abstract: A tubular pipe header is provided with an end surface which is substantially flat and in orthogonal relation to the longitudinal axis of the pipe header. An arcuate surface of a cylindrical transformer tank is provided with an aperture having a configuration at least a portion of which closely matches a portion of the end surface of the pipe header such that the matching end surface of the pipe header can be moved into the aperture when alignment therebetween is obtained. Another portion of the aperture includes non-matching means which prevents another portion of the end surface of the pipe header from moving into the aperture when alignment is obtained. In one embodiment, the non-matching means comprises tabs located in the same arcuate surface as the aperture. The tabs extend into the aperture. In aligning, the end surface of the pipe header is aligned with the aperture.