My guess would be right handed threading. Right handed threading means turning to the right will make the cog screw on and turning to the left will make it come off; Left handed threading means turning to the left will make the cog go tighter and turning to the right will loosen the cog. If you're really interested on where this comes from it's based from the math/physics based right- and left-hand rules
Most cogs and freewheels will thread on the direction of pedal drive.
Fixed hub lockrings are left threaded for obvious reasons. No lockring is necessary on a freewheel equipped bike since there is no drive force to loosen the freewheel when turning the pedals backwards.