A worker broke his finger while removing the screw pin on a shackle. Three workers were loosening the screw pin on a bow shackle that was attached to an excavator. One of them used a pin bar to loosen the screw pin. The shackle was unsteady, so a second worker came to hold it but was unable to keep pressure on shackle. A third worker put pressure on the shackle to help steady it but lost his grip, pinching his fingers between shackle and the attach point on the excavator.