Eternity band

Both styles carry a line of similar stones. The difference is how far the line goes. A full eternity band has stones around the entire ring. A half eternity band, sometimes called a half eternity ring, has stones across the front and a plain section of metal at the back.

The choice affects fit, care and what you can change later. The plain section is also why the half style is usually the easier one to adjust.

The setting decides how the stones are held, how much of each stone shows and how the ring wears. Three are common in bands.

• Channel. In a channel setting the stones sit in a row inside a groove, with a metal wall on each side. GIA's guide to melee notes that the setting has no beads or prongs. See channel setting.
• Pavé. Pavé packs many small stones close together, so the surface reads as one field of sparkle. See pavé setting.
• Prong. Each stone is held by metal prongs. GIA suggests having the prongs of an engagement ring checked about every six months. See prong setting.

GIA also describes a bar setting, which holds stones between upright metal bars. Ask which setting a band uses, because it affects both the look and how often it needs inspecting.

A jeweller normally resizes a ring by cutting the shank, then adding or removing metal. In a full eternity band the stones continue round the shank, so there is no plain section to cut. Ganoksin, a jewellery-trade technical reference, notes that rings with stones cannot be stretched on a mandrel, because of the stress it puts on the stones, and that the stones are taken out when a gem ring's shank is cut. Eternity and anniversary rings, meaning those with diamonds around the entire band, can be very difficult to resize, and pavé and channel settings generally cannot be resized easily.

So size matters more here than with a plain band. Get measured by a jeweller before you buy, and see the ring size guide and the ring size entry. GIA also advises extra care when a band is wide, noting that bridal sets wider than 4 or 5 mm when the band and engagement ring are worn together need special consideration. If you are unsure of the size, a half eternity band is the lower-risk choice.

GIA's stacking guide notes that couples increasingly add an eternity ring as a third ring, often to mark a significant anniversary. Others wear one as the wedding band. GIA's advice on wearing an engagement ring and wedding band is that how you wear them is up to you.

If you wear it with an engagement ring, a few details help the two sit well together:

• GIA advises making sure the silhouettes match and the rings fit together.
• It suggests pairing a thin, detailed band, such as a micro-pavé band, with a larger engagement ring so they do not compete.
• Mixing metals can lead to uneven wear. In GIA's example, a 14K gold band worn with a platinum one risks damage over time, because platinum is the harder metal.

See how to stack rings and the guide to choosing a wedding band.

Start with the size, since it limits your options. Then work through stone size, matching and care.

A band is often described by its total carat weight, which adds up every stone. A 1 ct total could be many small diamonds rather than one stone, so ask for the number of stones and the size of each in millimetres. Ask whether the stones are matched in colour, because a line of stones shows any variation. Check the metal against your other rings: GIA's example is that platinum is harder than 14K gold, so the 14K band can wear.

A custom band can be made to your size and stone count. The design studio is a place to start, and the wedding bands service covers bands to wear with an engagement ring.