How to read metal ring measurements
Distinguish the usable opening from the size across the outside.
Find the label beside the measurement
The Master Series Trine set publishes inner diameter and thickness separately. A size printed as 45 mm without a label may describe something else. Ask for the clear inside opening before comparing the two.
Check nonround shapes separately
For a contoured ring, ask for the inside dimensions across both axes. For an open-sided design, the gap is a separate dimension and may not be listed. Do not estimate either from a photo.
Confirm the selected SKU
A multi-size set may show only one size in the option selector. Compare that selection with the written package contents and confirm the discrepancy before buying.