What is a thrust washer? - Model Railroader Magazine

I am powering the rotor on an Athearn BB Rotary Snow Plow and just behind the plastic retention tube piece that sits at the end of the rotor shaft is a "thrust washer", as per the original diagram. When I researched it online, it just looks like a plain old metal washer. Is this something special, or can I just assume it is something I can pull from my small parts inventory? Cedarwoodron