Sliding aluminum window roller

The roller is on the right in the photos. As you can see it is tiny. It is a wheel about 5/16" in diameter with short axel protruding slightly over 1/16" on each side. On the left is a plastic place holder. The assembly is held in place by a 1 inch screw which also serves to hold the window frame together. The window uses 2 rollers, one at each end on the bottom. These windows were installed about 1970 in Camarillo, California.

Thanks for your help.