This part of ISO 16757 describes the modelling of Building Services product geometry. The description is optimized for the interchange of product catalogue data and includes shapes for representing the product itself, symbolic shapes for the visualization of the product s function in schematic diagrams, spaces for functional requirements, surfaces for visualization, and ports to represent connectivity between different objects. The shape and space geometry is expressed as Constructive Solid Geometry (CSG) based on geometric primitives concatenated to boundary representations by Boolean operations. This part of ISO 16757 uses the applicable primitives from ISO 10303-42 and from ISO 16739 and adds primitives which are required for the special geometry of Building Services products. For symbolic shapes, line elements are also used. This part of ISO 16757 neither describes the inner structure and internal functionality of the product nor the manufacturing information because this is typically not published within a product catalogue. Building Services products can have millions of variant dimensions. To avoid the exchange of millions of geometries, a parametric model is introduced which allows the derivation of variant-specific geometries from the generic model. This is necessary to reduce the data to be exchanged in a catalogue to a manageable size. The parametric model will result in smaller data files, which can be easier transmitted during data exchanges. The geometry model used does not contain any drawing information such as views, line styles or hatching.