@AmLachDesigns is correct. This 'parts' definition is a bit new for us designers here at Shapeways, so we need to get used to a new term.
A MESH or SHELL is an independent closed surface. It must be manifold, watertight, etc. There can be more than one of them per file
A PART is one or more meshes that will "stay together". That includes intersecting meshes, but also includes non-intersecting meshes. That means that interlinking loops (chain mail), but also includes things that are caged, etc.
This model:
http://shpws.me/oIBC is considered to be "one part". Even though the 80 rings are "loose", they are "trapped" by the cage around them, and won't come free inside the printer.
This new definition would also include a box with only 1mm holes that is filled with 2mm spheres. - if the spheres can't escape from the box, then the assembly can be considered to be one single PART.
I'm rather proud to say that this model
http://shpws.me/oBCu is ONE part. It has FOUR rotating axles and the two large sets of tires are on swing arms that will rotate up and down, all within about a half inch cube. The shells are separate, and can move freely, but it's considered to be ONE PART.