I've never heard of a 4s or a 6s motor, I could be wrong. There are 4s/6s lipo packs.
brushed and brushless motor are rated by turns 10t 13.5t 3.5t or for some brushed 13x2 would be a 13 double.
Hope this helps
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Also in electric aviation and high velocity cars you'll see motors driven by 4s or 6s LiPO packs, which have very high voltage.
Generally a high voltage motor has more turns of thinner wire than a motor designed to make roughly the same power from a lower voltage, say the standard 2s LiPO in RC cars. Otherwise the high voltage motors would fry from over-current in the windings. A high voltage motor is more efficient at converting energy to work (wastes less energy as heat) and therefore is preferred for systems where the voltage source is not a design constraint.