That description fits a sewing gauge—often called a buttonhole or hem gauge.
🧵 What it is
It’s a small tool used in sewing with:
- Numbered notches → for consistent spacing
- A rotating top plate → to lock in or adjust measurements
These were especially common in older sewing kits.
✂️ What it’s used for
- Marking evenly spaced buttonholes
- Measuring and folding hems
- Repeating the same distance quickly without re-measuring
- Helping keep stitching neat and consistent
🤔 Why it looks unusual
- Many vintage versions were standalone tools (no attachment needed)
- The rotating part lets you set and repeat measurements
- Designs vary a lot, which makes them look mysterious
🧠 Bottom line
You likely picked up a vintage sewing measuring tool—simple, clever, and very practical for consistent spacing in fabric work.
If you can describe the material (metal, plastic, wood) or size, I can help identify the exact model or era 👍
