are all the brush sizes the same? or are they diff according to make? im refering to the 1/10 scale motor for the HPI's.

Modified motors have standup brushes and stock motors have laydown brushes.

How can i tell which is which?

Motors that have stand up brush hoods are taller and lay down brush hoods are wider . Most brushes are labeled stand up or lay down . Most stock and some 19T motors are laydown and mod motors are stand up .