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The STEP file (Standard for the Exchange of Product Data) format is a great format for exchanging NURBS engineering data. It is a popular engineering programs such as CATIA, Creo, SolidWorks, NX, Inventor, etc. STEP will exchange the NURBS Solids and the Part and assembly project structure into Rhino.

Part and Assembly files structures are quite different from Rhino's layer based structure. but in a project situation retaining that organization of parts and assemblies can be beneficial. Rhino translates parts and assemblies into Blocks and block instances.

Rhino supports a series of STEP Application Protocols (APs). Each AP contains different levels of information.

* AP203 - ConfigControlDesign. This is the default format. AP203 defines geometry, topology, and configuration management data of solid models for mechanical parts and assemblies. Primarily supported by aerospace and defense. Configuration controlled 3d design of mechanical parts and assemblies.

*AP214 - AutomotiveDesign. Popular for automotive industry mechanical design processes. Includes AP203 plus colors, layers, GD&T (geometric dimensioning and tolerance) and design intent.

*AP214 - AutomotiveDesignCC2

*AP242 - Newest standard that merges STEP AP 203 and AP 214 to create a single standard for model-based 3D engineering.Display Performance and CPU Bottleneck: Rotating the view, zooming or panning very slow even with a nice graphics card.