
Technic snowmobile
has a multi-component tread formed from many individual links. While LEGO has made tread links before, these are much wider, have small cleats on them (should work much better on the carpet), and perhaps hold together better than the old style. More to the point the length of this tread system is very adjustable, leading to variable length treads. Bravo LEGO! I don't have these (yet...), but someone has put up some more detailed pictures up on Brickshelf:
Brickshelf gallery of Technic snowmobile
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Brian Davis