Plastic re-usable UK ring sizer

Brand: www.multisizers.com

Instructions for use:

"The Multisizer Ring Gauge works like a belt. Simply push the end through the buckle to form a ring shape.

Slip the ring sizer on to your finger and adjust to give it a comfortable fit, checking that it just slips back over the knuckle. "

The example shown on the packaging illustration indicates a size O