Wheel and bearing, Plastic Thrust Washer
 

Just replaced the whole new wheel bearing hubs and rotors on both of my front wheels. Just wonder what is that plastic washer between the spindle and bearing is there for?
I have a manual hub locking.

I wasnt bother to put them back on when i installed a new bearing hubs. But I will have to get a new brake calipers install. So just wonder if I shall put these thrust washer back on?