Abstract: An apparatus is provided for enabling selected structure to be joined to a pherical segment, such as a segment employed as a lens, viewing port or radiation transmissive housing. The apparatus includes a structure support component which is insertable into an aperture through the segment, the aperture being circumscribed by a frustoconical bearing surface, and the support component being provided with a frustoconical seating surface which matches the bearing surface of the aperture. A retaining component positioned inside the spherical segment is provided to selectively secure the support component within the aperture, so that the frustoconical bearing and seating surfaces are maintained in abutting relationship. Several components of a compliant nature are selectively positioned between the support means and various portions of the spherical segment, proximate to the aperture, to seal the spherical segment from external pressure, which may become substantial.