I recently attached a trailer tying ring (3 1/2" x 3 1/2" d-ring with loop pressed into the hardware mounting plate) from a roof truss in a storage unit. The ring is rated for 1000+ pounds. My purpose was a boat motor lifting system. It worked great with an attached block and tackle and was effortless. Since I attached the ring system vertically to a roof truss stud, the ring holding rating capacity may be lower since the weight is now suspended by two 3/8" lag bolts that are attached with a backup plate and compression on the 2 x 4. Can someone give me a reference for calculating the holding power of such a system? Thank you.