Guide Rail Sled would translate better... ;D
It does work well. It may not be totally obvious until you get more aquainted with the set but there is a little "foot" that is used to level the router if one side of the router base is elevated because it is sitting on the guide rail. It also helps in a number of other situations where one edge of the router base in hanging in air.
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There are two pieces, each of which can engage the top of the guide rail, that connect to one another with a micro-adjustment. These can be configured in many ways relative to each other, the guide rail, and the router. The plethora of combinations makes this a really versatile set up.
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I forgot to mention that the rods come with the router.
Tom