Is it possible to create a custom ring that is adjustable or expandable?

Yes, but not in the way most people mean when they ask. Let me save you some time upfront: if you want a ring that can be adjusted from a size 5 to a size 7 without going to a jeweler, you're looking at a mechanical solution - a shank with a hinge and a clasp - and it will never feel quite like a solid ring. It's a workaround, not a feature.

The more common version of this question comes from clients who expect their ring size to change - pregnancy, arthritis, age-related knuckle swelling. For that, the real answer is sizing, not adjustability. Most rings can be sized up or down by a full size or two if the shank is plain metal and the stones don't run all the way around. If they do, you're in a different conversation.

The two real approaches

Hinged shanks and clasps

This is the traditional "adjustable" ring. The shank (the band part) is cut and fitted with a small hinge on one side and a snap-lock or a screw mechanism on the other. You open it to get it past a knobby knuckle, close it for a snug fit. I've made maybe a dozen of these in twenty-two years. They work. They also add about $400 to $800 to the fabrication cost, they collect soap and lotion, and they're a bear to clean. One client named Priya came back after six months because the clasp kept popping open when she grabbed a dog leash. We fixed it, but she switched to a simple sizing job on a different ring within a year.

Sizing cells and spring bands

These are internal mechanisms - a small spring-loaded coil or a tiny silicone insert - that sit inside the shank and let the ring flex a quarter- to half-size. They're useful for minor swelling. I've used spring shanks from Stuller for clients who work in jobs where their hands change size by noon every day. They're not invisible. You can feel the mechanism against your finger. And they add about $150 to $250 to the cost. For most people, a traditional sizing job is cleaner.

What you actually want to ask

The question people should be asking is "How much can this ring be sized later?" That's the real design constraint. A plain 2.5mm half-round 18k band can be sized up or down two sizes without the metal distorting. A full-eternity band - diamonds all the way around - can't be sized at all without resetting every stone. A three-quarter eternity can move about half a size. A ring with a thick, carved shank or heavy milgrain? Maybe one size, and you'll lose the detail on the sizing seam.

I tell every client the same thing: if you think your finger is going to change size, don't put yourself in a position where you can't fix it. A solid, plain shank with a simple 4-prong or bezel setting is the most adjustable ring you can own. Everything else is a compromise.

The short version

Adjustable rings exist. They're not better than a well-fitted solid ring. They're a solution for a specific problem - arthritic knuckles, pregnancy, jobs that change hand size. If you have one of those problems, a hinged shank or a spring band is a good answer. If you don't, save the money and the complexity. Get sized properly, buy the right metal, and plan for a future sizing if you need one.

And for the love of everything, do not buy one of those expandable shanks you see on Etsy with a gap in the bottom. They will catch on everything, they will snag your sweaters, and they will turn the prongs sideways on your center stone. I've fixed three of those this year alone.