What do the numbers stand for on motor sizes?

For example what is a 380 motor? Does it stand for anything specific? Like milli horsepower or something?

These days they are mostly to give you a general idea of how powerful they are with out much real reference. The origional was the "speed 400", where 400 referred to the size of the motor case. Other motors are often in a simular case, but given higher or lower numbers in reference to the expected power.

But it's nothing as useful as a direct measurement of power.

An excellent reference to all of this can be found [link=http://www.mabuchi-motor.co.jp/en_US/technic/t_0100.html]Here ( click me! ).[/link]

Mabuchi manufactures most of the brushed motors used in mechanical devices, and then adapted for RC flight.

Their nomenclature ended up being a norm in the RC world, until brushless took over.

The 340, 400, 450's, 550's, 600's references all came from their naming...

Thanks guys