http://wiki.bowlingchat.net/wiki/images/c/c6/GradientLine.pdf

or

https://www.youtube.com/watch?v=c93ZRsWbF7U

In my opinion and others may differ, you would drill out the Mass Bias with the largest legal hole you can drill (1-3/8 I think).  That with a 3 3/8 pin to pap drilling on a symmetric ball.  I have heard arguments that on an asymmetric ball that flare can be increased by going further than 3-3/8 ... but there are others that disagree with those statements.  I am not going to get in the middle of that argument. 

Of course doing this may make the ball illegal, so someone who knows what they are doing needs to make sure you have legal static weights when done.

Additionally, Mo has a layout called the double thumb layout which is considered the highest flaring layout possible ... at least that I know of.

Other arguments state that increasing the differential beyond the legal 0.06 limit has very little effect on the hook potential of the ball.  Sort of like diminishing returns. 

In Brunsnick's video the largest flare increasing hole isn't on the gradient line, but basically perpendicular to the gradient line (unless you have an unusual PAP).  The P4 hole would be closer to the 2 -1/4 down the VAL line drilling in the video.

So like I say opinions vary.  Probably not the answer you are looking for.  I think either the P4 hole or the 6 3/4 hole would give you a large amount of flare, even if it technically isn't the largest possible. 

Either way you want the biggest hole that is deep, because you want to take out part of the core.  Essentially changing the shape of the core to a taller skinnier shape.

I'm sure someone will correct me if they disagree.

Rick, I am looking at a symmetrical ball with a low Differential of .023 and 3" of flare in a 13# ball. I do better with balls with differentials in the area of .045 or a bit less to .055. ... So the reason for my question is to see if I can raise the Differential and flare on this low Differental - low flare ball and how much.

Would that 6.75" x 3 3.75" wt hole get me close to .045 differential or a bit less maybe?

Or why are using this ball if it's not really what you want diff wise?

Is it new?

I would lay it out with a similar favorite layout and throw it first befor adding a weight hole to adjust reaction...

Worry less abt the flare and more abt what you want the ball to do...if you wanting play and down & in shot I would do weird a 4-4.25" pin to pap and then throw it...if you need more reaction either adjust surface and/or add a adjusting weight hole