Over 75 parts in part groups including Technic pieces and Mindstorms NXT components. Everything is modeled to 1:1 scale within roughly 0.5mm tolerance with respect to the real parts. Snapping helper points are modeled with very high precision. Here are some tips to make using these models easier:
1) Set Window -> Model Info -> Units -> Enable Length Snapping to 4mm.
2) There are two detail layers for many models. Use "HiFi" for the most detailed versions and "LoFi" for better interactive use while modeling.
3) There is a "Helpers" layer that includes line segments that exactly model where connectors and axles fit with beams and bushings, etc. Turn on this layer and x-ray mode for precise "snapping" of parts.
Visit the discussion group for instructions on how to download all parts in this collection organized for use as a SketchUp component library.