Ok, my grip photos...

[Monte]

Hat tip to bowl1820 for the link to explain how to do this.

I sent these photos to an online bowling retailer. They told me it appears my span is too short, and that's what's causing me to "grip" the ball, and therefore develop the blister on my thumb.

Here are the pics:

1. Thumb fully seated
https://s24.postimg.org/sf3bwy8jp/image.jpg

2. Span (though this is a bad photo I may need to re-take)
https://s24.postimg.org/ukxmrgc05/2.jpg

3. Gap between hand and ball
https://s24.postimg.org/z83ot7zd1/3.jpg

[Monte]

Continued...

4. Fingers in finger holes
https://s24.postimg.org/jb4wwi6yt/4.jpg

5. Palm, facing down and from behind
https://s24.postimg.org/55z3uoxxh/5.jpg

6. Ball upright, like I would hold it on the approach
https://s24.postimg.org/nmtilidvp/6.jpg

7. Blister location
https://s24.postimg.org/jrq4ixupx/7.jpg

So it appears that the span is a problem. I don't know if I should go to my local pro shop and get re-measured, or go to a different one. I'm considering going to a different one, because the guy who has the pro shop here is never there when I go, and I was thinking a pro shop that services a larger area might do a better job. I dunno.

[YODA]

To me photo #3 gives it away right off the bat. Too short IMO which is causing you to try and hold the ball and use thumb pressure which on release is causing the blister. Again I am not a pro but thats how it appears to me :)

[bowl1820]

With your thumb inserted in the thumb hole and laying your fingers across the holes and your hand relaxed, the half way point between the first and second joint should be at the gripping edge of the hole. If your using inserts it's the gripping edge of the insert not the drilled hole.

http://s5.postimg.org/60yijdbyf/fit_Bowling_Ball_Parts.gif

See at the 17:45min. mark in the below video.

Just to double check,

With your fingers laying across the holes, hold the ball like your going to roll it. So that it settles into your hand, then without moving your hand.

Example:
http://s5.postimg.org/ac7neq07b/span_02.jpg

Rotate the ball back up so you can see where the edge of the holes are in relation to the midpoint between the two joints. (or get a picture form below like this one.)


Getting Fitted at a Bowling Ball Pro Shop USBC Academy


https://www.youtube.com/watch?v=TY_-2mXCrXQ

Photo #7:
A blister at the base of the thumb usually indicates:
Span Too Short or Too Long
Hole Needs More Bevel
Hole Too Big

http://www.jayhawkbowling.com/Pro_s_Corner/Fitting_Tips/fig6.jpg

[Monte]

With your thumb inserted in the thumb hole and laying your fingers across the holes and your hand relaxed, the half way point between the first and second joint should be at the gripping edge of the hole. If your using inserts it's the gripping edge of the insert not the drilled hole.

http://s5.postimg.org/60yijdbyf/fit_Bowling_Ball_Parts.gif


Confirmed.

Went bowling again today. I had to severely modify (so I didn't blister again), which I think took some hook off the ball because I had to play a more severe "outside-in" line, but I looked closely at things when I first inserted my thumb in the ball.

Just eyeballing it, I'm between 1/8" and 3/16" too short on my span.

The pro shop guy at my local center isn't there every day, and I think he's rarely there on weekends. I think he owns the shop as well as the bowling center. Though to fix this I'm thinking about going to a different pro shop.