This is from Power House training,
Fingertip Grip Finger Pitches:
For a right handed bowler :
Middle finger-1/8" Left
Ring finger - 5/8" Right
For a left handed bowler:
Middle finger - 1/8" Right
Ring finger - 5/8" Left
This is based on the relationship between the fingers and thumb.
Very few bowlers will require something different than these; again you need to drill what you see if that is the case.