# 4.5.1 Selecting the thumb hole shape (Round or Oval)

<span style="font-family: monospace; color: #6b7280;">4.5.1</span> <span style="border: 1px solid #d1d5db; color: #4b5563; padding: 2px 8px; border-radius: 3px; font-size: 0.85em;">thumb</span>

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.

### Related Sections

- 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.