by interlocking of projections or inserts with indentations, e.g. of tongues, grooves, dovetails

Full Title

Walls, e.g. partitions, for buildings; Wall construction with regard to insulation; Connections specially adapted to walls (connections for building structures in general E04B1/38; insulation for buildings in general E04B1/62; building elements of relatively thin form for parts of buildings E04C2/00) > built-up from layers of building elements > Walls having cavities between, as well as in, the elements; Walls of elements each consisting of two or more parts, kept in distance by means of spacers, at least one of the parts having cavities > using elements having specially-designed means for stabilising the position; Spacers for cavity walls > by interlocking of projections or inserts with indentations, e.g. of tongues, grooves, dovetails