I happen to have a a screw with an eye sticking idly in my living room ceiling, and I'm thinking about using it to hang a rope for bodyweight rows etc. The screw is 8mmx50mm (thread x length of anchor). The TRX ceiling anchor seems to use 2 screws with 10 mm thread, so I'm a bit concerned about using my screw as is. On the other hand, the TRX product may be vastly overengineered and I have hung my 100kg from my screw a few times.
Now my question: Is the setup described above (2 screws, 10mm thread) typical for sling trainers? Are there experiences with using something closer to my thread size, one screw, in a concrete ceiling without the whole thing crashing down?
Note for imperialists, I mean folks unused to metric units: 8mm is 0.314 inch, the closest thread size in imperial units is probably 1/4 inch.