(under subclass 245) Structure in which the curvilinear barrier is formed of plural layers which are facially opposed.
SEE OR SEARCH THIS CLASS, SUBCLASS:
561+, for a barrier of laterally related, individually assembled courses and see the search notes under subclass 561 for other constructions involving plural layers.
SEE OR SEARCH CLASS
138, Pipes and Tubular Conduits,
114, for plural coaxial ducts and subclass 148 for tubular structures having plural spaced layers and see the reference to Class 138 in the class definition of this class (52).
