CBD 510 Batteries are used for vape cartridge specially,Which's thread size all is M7*0.5(mm),so as to make sure the batteries can fit all CBD vape cartridges's thread.
Now the 510 batteries mainly have 3 types:
Round shape, inhale to work (Constant voltage 3.6 or 3.7V outputs)
Round shape,button to work(with pressure regulation and preheating features)
Other shapes, more functions(For example: box shapes,Hidden design,Designed with display,ect. )