I inherited this piece which is why I can place its general age as 1930s. This is a size 8-8½. After the early 40s my uncle couldn't have gotten this on his pinky and never ever wore rings in my lifetime. I do understand that in his youth he was quite the man about town and no doubt wore this to the races.
This ring is 10K yellow gold with a horseshoe shaped piece of black onyx. The ring weighs 5 grams. The onyx is in a combination of bezel and prong set and is very securely held in place, the bezel forming the top and bottom of the horseshoe and the prongs (2 on each side) are formed by something that looks like horse's brasses or maybe they are other horseshoes. (I'm not real knowledgeable about horse things.)
This ring is in excellent condition. All those marks in the photo are dust and over-magnification. Nothing is visible to the naked eye. The ring is marked 10K inside and there is plenty of gold on the back for sizing if needed.
I referred to this as a man's ring but I have worn it on several occasions on my middle finger. It is a little overpowering for me however so I'd like to pass it on to someone who will enjoy it more. Comes in jeweler's ring box but not the original box.