So for open bowl i need a medium to light oil ball to keep a more consistent score on my ths shots?
Kyle,
There probably isn't any one correct quick answer to your question because for open bowling, you could be facing lane conditions from bone dry (last oiled a week ago) to a heavy long oil pattern that was put out for a tournament but the lane was not used for the tournament so you are the first to bowl on it. That's not even taking into account that each bowler has their own unique style and each bowler's definition of heavy, medium and light varies.
For a quick answer, not knowing the lanes or your style, this might work:
If you are bowling on a fresh THS pattern, a medium oil ball (generally) should be good. If you are open bowling after leagues on a THS pattern, a light oil ball (generally) should be good.
Someone else may offer a better answer than mine.