Manufacturer's designation:

MR84

Construction:

A ball bearing consists of two rings (inner and outer) and rolling elements (balls) connected by a cage.
Open (without any seals on both sides). 

Application:

conveyors; robotics; 3D printers;
dental equipment (heads, drills);
skateboards; roller skates;
boat propeller shafts;
DC electric motors; electric blowers; electric saws;
toys; models of helicopters, airplanes, cars;
drones.