A full eternity band is set with diamonds the whole way round, so it sparkles even when your palm faces up. A half eternity design puts the diamonds across the top and leaves the lower half as smooth metal. Seen on the hand from above, the two look almost the same. The differences show up in daily wear and in what can be done to the ring later.
If you want the most diamond and your size has been stable for years, the full version delivers it. If your fingers swell in hot weather, you are planning a pregnancy, or you simply like keeping options open, the half version is the practical pick.
Order the exact size, because a full circle of stones is hard or even impossible to resize. Sizing a ring means cutting the shank and adding or taking out metal, and on a full band there is no bare stretch to cut: every section holds a stone. With a half style, the plain lower half gives a jeweler room to adjust.
Measure late in the day, when the finger is at its largest, and measure twice. Rare Carat makes that easy: request the free ring sizer and check the result against the step by step guide linked in the FAQ below, using the finger the band will actually sit on. Buying from home is less of a gamble with free returns within 30 days at Rare Carat, so a band that does not sit right can go back.
Both are real diamonds. A stone grown in a lab is crystallized carbon like a mined one, with matching hardness and brilliance, and only a lab instrument can separate the two. The difference is cost: lab grown stones cost far less at the same size and grade, and on a band holding a whole circle of diamonds that gap adds up quickly. Mined stones hold their value better if you ever sell.
If you want bigger stones around your finger for the money, read how lab grown diamonds compare before you choose. If resale or tradition weighs more for you, natural is the safer route.
Most people wear it below the engagement ring, closest to the palm. Line it up with your center stone and look at how the two meet: a straight band can leave a small gap under some heads, and with a row of diamonds that gap is easy to spot. Slim versions also stack two or three high, or work alone as an anniversary ring. If you are buying both rings together, choose the engagement ring first, then size the band to sit beside it.