I don't really understand what your question is. But it's absolutely safe to Rotafix a cog onto a freewheel hub without a lockring. The leverage you can achieve is enough to rip the threads clean off the hub if you overdo it. Skidding the rear wheel will not loosen the cog. I've ridden nearly 30,000 miles on Rotafixed cogs and never had one come loose, due to my preference for quick release instead of a nutted axle.