The phrase "a thumb ring" is correct and usable in written English.
You can use it when referring to a type of ring specifically designed to be worn on the thumb.
Example: "She wore a beautiful thumb ring that complemented her outfit perfectly."
Alternatives: "a ring for the thumb" or "a thumb-sized ring".
Despite all difficulties they face in the Islamic Republic, some them signal their gayness discreetly by wearing a thumb ring or a rainbow wristband.
A jittery, good-looking young man, he wore a gray cashmere V-neck sweater with no shirt under it and a thumb ring.
Ms. Stone decided that her character would always wear a thumb ring — two white gold Ice Cube rings with diamonds — and a diamond-encrusted ring with a heart-shaped pink diamond at its center.
Cropped grey hair, clean shaven, a soft Yorkshire lilt and not a thumb ring or dreadlock in sight.
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There might be a thumb ring.
"Does your hand hurt from all that writing?" someone asked, as Roberts, wearing a Celtic thumb ring (she also has a Celtic tattoo on her ankle), scrawled her autograph.
Vendola, who favors sharkskin suits and wears a gold thumb ring on his right hand and a diamond hoop earring in his left ear, has built a massive youth movement.
The positioning guide consists of a rack with an attached thumb ring to allow the operator to hold it stationary with respect to the patient.
Thank you so much -- with a sweet, sweet thumb ring on it.
It doesn't matter what it is, there is likely to be some sentimental or emotional reason you wear a particular thing – in my case, I wear my mother's wedding ring on my right hand, and a battered, misshapen silver thumb ring, bought for me by my youngest daughter with her 50p pocket money.
