This is a 40cc bottle of Kyosho 40,000wt (#40000) Silicone differential oil for 1/8th scale off road buggies (and some 1/10th scale on-road touring cars). The thicker the oil, the less your differential will "diff out" in the corners, where the two tires will turn at different speeds. Changing the diff oil in your diffs is one of the most important tuning options for off-road buggies.
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