That’s a V-groove wheel / gate roller pulley
What it is:
Heavy duty steel wheel mounted in a U-shaped bracket. The groove is V-shaped so it runs on angle iron/track. That yellow/gold finish is zinc plating - stops rust.
From your pic:
1. Type: V-groove roller - the "V" fits 90° angle iron perfectly
2. Mount: Bracket has holes for bolts. Top has rivet/axle holding the wheel
3. Size: Looks like 3-4" diameter wheel. Common for gates/doors
4. Finish: Zinc plated = outdoor use, weather resistant