There's a paragraph or so in the BR.com Unofficial FAQ section which describes Radius of Gyration (RG). 

It says that the following scale is used for low flare protential balls:

Low RG = 2.430 to 2.540
Med RG = 2.541 to 2.690
High RG = 2.691 to 2.80

And in the last paragraph it states the following:

"A low RG ball will be easier to "rev up" and it will rev faster quicker because most of the mass is located relatively close to the center of the ball. Since it revs faster sooner, it also wants to hook sooner. Medium RG balls are intermediate-length balls. They are a little more difficult to spin (takes more power) so most bowlers will see a slight loping characteristic through the heads and early midlane followed by a faster revving action and later hook--than you would get with the low RG ball. High RG balls are the hardest to rev up since the mass is concentrated farthest from the center and therefore bowlers will see longer lope, much later revving up, and the latest hook from these balls."


So my questions are:

1.)  Is there a different scale for medium flare and higher flare potential balls or can this scale be applied to all bowling balls ?
2.) Does one need to consider the differential ?
3.) Based on the last paragraph, if I wanted to play down and in -or- a more direct line to the pocket, I shoud use a ball that has a high RG, correct ?


Thanks for the answers.

Elimeno has it pretty good there.  However, specifically answering your last question, it really doesn't matter what you use playing down and in, that more depends on your lane conditions.  If you have a slick, long pattern, that will have the effect of making the ball go longer and turning sharper on the backend, if you have a ball that already does that, you're in for an over/under nightmare.  I would use a low rg, high diff ball for wetter conditions, and a higher rg, lower diff ball for drier conditions.  Balls are usually designed that way anyway.  The lower the rg and the higher the diff, the more hook potential a ball will have, generally speaking.  Most companies also put flare potential with the core specs, so it's easy to look at and see.  But generally yes, the lower the rg, the higher the diff, the more a ball will flare.