Maintenance employees were working on the leg quarter conveyor belt. They made and placed a steel bracket/guide above a chain like belt where it made a 20-30 degree bend around a corner to prevent the belt from popping off. While the belt was running, the injured employee saw there was a rough edge on top of the bracket/guide, so the employee reached to feel the top of the bracket/guide and his hand was pinched between the belt and the guide. His left thumb was amputated above the knuckle.