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4.5.1 Selecting the thumb hole shape (Round or Oval)

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 size. Everything else in the thumb workflow — pitch and insert entry — is the same either way.

⚠️ Two-handed and thumbless bowlers: If a bowler is set as two-handed or thumbless in their profile (see 3.1.2), Spectre Cloud removes the thumb section from the spec sheet entirely. There is no thumb hole to input — the shape selector, thumb size, thumb pitch, and thumb insert fields simply do not appear. The rest of this chapter applies only to bowlers who use a thumb.

🎳 Round vs. Oval — What Actually Changes

Round and oval thumbs are drilled and recorded almost identically. The single point of difference is how the hole's dimensions are specified:

  • ✅ Round — the hole is defined by a single size value. This is the most common choice and the simplest to enter (see 4.5.2).
  • ✅ Oval — the hole is defined by four oval inputs: starting bit, oval width, oval degree, and taper. These feed Spectre Cloud's oval calculation (see 4.6.1 and Book 05).

Beyond hole size, the two are the same: you enter the thumb pitch in the pitch tiles (4.5.3) and any thumb insert details (4.5.4) exactly the same way for a round or an oval thumb.

🛠️ Selecting the Shape in Spectre Cloud

  1. In the spec sheet, go to the Thumb section.
  2. Set the thumb hole shape to Round or Oval.
  3. The size fields update to match — a single size field for Round, or the four oval input fields for Oval.

⚠️ Verify with your Spectre team: confirm the exact UI element for the thumb shape selector (toggle, dropdown, or radio) and whether Round is the default on a new spec sheet.

Note: Oval is the right choice when a bowler's thumb doesn't sit cleanly in a round hole — the oval follows the thumb's natural shape and rotation. The four oval inputs are covered in 4.6.1; the calculator mechanics live in Book 05.

  • 4.5.2 — Entering thumb hole size (Round)
  • 4.5.3 — Entering vertical and lateral pitch for thumb
  • 4.5.4 — Thumb insert type and size
  • 4.6.1 — Selecting an oval thumb: starting bit, oval width, oval degree, taper
  • 3.1.2 — Bowler profile: handedness and grip style (two-handed / thumbless)
  • 05 — Oval Calculator (full oval mechanics)

Tip: Because only the hole-size step differs, don't think of round and oval as two separate workflows — it's one thumb workflow with two ways to size the hole. Pick the shape first, size the hole the matching way, then proceed through pitch and insert as normal.

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