[Sammus]

the 1y and 2.5d etc are how many winds the motor is made with, along with the termination (ie how the winds are joined tgether). Basically, more winds = lower kv, higher torque. Y termination = lower kv higher torque than D termination

I think there are so many differences to basically get a lot of kv options with all the different size motors, then you choose the wind with kv to suit the batteries you plan to run. neu's are rated to 60,000rpm, but i think their optimal efficiency is around 50,000rpm so you dont want to have it revving much past that. I'm pretty sure on all that, I dont own one though and am working from memory from research i recently did, im sure someone will chime in and correct me if im wrong :P