I have a load point attached to building roof rafters; what's the working load?

It's a flat roof, with a layer of plywood and then asphalt and gravel. The rafters are true 2x8s. The rafters in this section span 14FT. The load point is a long iron bar formed into a "ring", attached to a thick bolt through the top 1/3rd of a rafter. The rafter is then load-supported to the two adjacent rafters using iron bar. Rafter spacing is 16IN. The bolt, ring and bar are all formed from 5/8IN iron. Hence, the load is spread over 3 rafters. I'm going to attach a chain fall or hoist to this load point. Now I want to know the working load limit of the load point, just like I have one of the side of the chain fall.