This simple part can help spread the pressure from the toe stop nut onto the baseplate evenly, helping keep tension.

These parts aren't required on all skates, as some roller skates use Bolt-In toe stops like the Starfire 500. More advanced skates use a more advanced system which uses a pinch bolt to grip the plate onto the toe stop itself - like the Bont Hybrid Prodigy and Bont Quadstar Tracer skates.

Even plates with the lock nut don't strictly require a toe stop washer, but if your toe stops are popping off super frequently this can be a part to investigate that may lessen the frequency of them coming loose.