There is approximately 6mm of space in between the prongs from corner to corner, and should fit a round stone from around 0.75 carat to 0.90 carat. Measurements: Size : Finger size 4 Stone s:round diamonds 0.45 carat total weight. Estimated G color VS clarity Metal: Platinum 900. Platinum 0.75ct Diamond Halo Engagement Ring Setting Semi Mount size 4" is in sale since Wednesday, April 19, 2017. This item is in the category "Jewelry & Watches\Engagement & Wedding\Engagement Rings\Settings Only".The seller is "tmgems" and is located in Larchmont, New York. This item can be shipped worldwide.