Abstract: Structure supporting apparatus which for a particular nominal size can be interchangeably sealingly clamped and centered between bolted flanges of varying pressure rating and design standard. The apparatus includes at least one support member having opposite parallel sides for sealingly engaging the seating surfaces of the flanges, a centrally positioned opening extending through the member and through the sides thereof for positioning structure supported thereby in alignment with the flow passageways in the flanges, the periphery of the support member being substantially square shape and including a pair of spaced apart recesses disposed in each of the four sides forming the substantially square shaped periphery thereof.