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4.5.1   thumb The thumb is the largest hole on the ball and the primary control point for the release. Before entering thumb measurements, the spec sheet asks you to set the thumb hole shape — Round or Oval. This choice affects only how you define the hole si...

4.5.2   thumb For a round thumb, the hole size is a single value entered on the spec sheet. The thumb section records both the O.D. (the drill/hole size) and, when a thumb insert or slug is used, the hole size the bowler's thumb actually sits in — the two are...

4.5.3   measurement Thumb pitch works exactly like finger pitch — you enter it into the pitch tiles around the thumb hole, and the tile is the direction. There's no direction to select from a dropdown. For the full mechanics of the pitch tiles, see 4.4.3; f...

4.5.4   thumb Many bowlers use a thumb slug or thumb insert rather than a bare thumb hole. This page covers recording the thumb insert on the spec sheet. The physical installation (drilling the pilot hole, seating, adhesive, finishing) follows your shop's sta...