They are very tiny round parts 4 in total any idea what for? It's the rivet counter.
I believe they are replacement roller bearing caps for the outside of the axles on the trucks. My HO SD40-3 came with those also. Really nice of Scale Trains to include those.
Ralph
Dan Stokes
My other car is a tunnel motor
stokesdaincluded with my crude oil tank cars from last year or so.
Russell