Clasp types, explained

A clasp older than its pearls

In the jewellery collection of the Victoria and Albert Museum in London is a necklace of two strands of graduated, knotted cultured pearls. They fasten with a rectangular box clasp set with a square emerald in a frame of diamonds. The museum's own note on the piece is brief and rather telling: the pearls are fastened with "an earlier" clasp.

In other words, the clasp came first. Somebody thought it good enough to keep, and fitted it to a newer pair of strands. It is a neat reminder of where the engineering in a necklace lives. The chain or the pearls are what you see. The clasp is what you rely on, every time you put the piece on and every hour you wear it.

What a clasp has to do

A clasp has two jobs that pull in opposite directions. It must open easily when you want it to, often behind your own neck, by feel alone. And it must not open when you don't want it to, whether the piece snags on a jumper or simply moves as you do.

Every clasp strikes its own balance between the two, and most rely on one of four things to stay shut: a small spring, a screw thread, a magnet, or the weight of the piece itself pulling the two halves into place.

Spring clasps: lobster, trigger and bolt ring

These are the clasps you will find on most chains. Each has a tiny spring inside, and a lever or gate that you push to open it. Let go, and the spring snaps it shut.

• Lobster clasp. Named for its shape, like a lobster's claw. Press the lever and a gate swings in, hook it onto the ring at the other end of the chain, and release. Trade guides describe it as highly secure and easy to operate, and it is widely treated as the standard clasp for everyday wear. It is a little heavier than a bolt ring, which suits medium and heavier chains, where the chain's own weight balances the clasp.
• Trigger clasp. A rounder relative of the lobster with a wider opening, so it is easier to attach to a larger ring. It is bulkier, so it is used on heavier chains and pendants rather than delicate ones.
• Bolt ring, also sold as a spring ring. A small hollow ring with a lever on the outside. Pull the lever back and a section of the ring slides open. It is light, neat and inexpensive, and suits fine necklaces and bracelets. The catch, quite literally, is the lever: on small bolt rings it is tiny, and both trade guides here note it can be hard to use for anyone with limited dexterity.

Clasps held by weight: toggle and hooks

Some clasps have no moving parts at all. They stay closed because the piece hangs from them, and that simplicity is both their charm and their limit.

• Toggle clasp. A bar on one end and a ring on the other. Turn the bar sideways, pass it through the ring, and let it fall across. It is easy to handle, because both parts are large, and it is often made a decorative feature in its own right. It also works on the front of a necklace, where it can be seen.
• Hook and ring, and the T-bar. Variations on the same idea: a hook or bar that sits in a ring, held there by the pull of the necklace or bracelet. One UK supplier of jewellery findings advises that the hook needs a generous overlap with the ring.
• S-hook. A hook bent into an S, which connects two loops. Simple and easy to use, and often seen on handmade necklaces.

The same supplier makes the important point about all of these. Because weight does the work, they hold best on heavier pieces. On a very light chain there may not be enough pull to keep them closed.

Locking clasps: box, barrel and padlock

These clasps take a moment longer to close, and in return they are hard to open by accident.

• Box clasp. A flat tongue, folded so that it acts as a spring, slides into a small box until it clicks into place. To open it, you press the tongue and draw it out. Many box clasps add a safety catch on the side, a little hinged loop that closes over a peg for extra security. Box clasps are traditionally used on formal pieces and pearls, and the box itself is often set with stones, as on the V&A necklace.
• Fishhook clasp. A close cousin, often found on pearl strands: a hook slides into an oval box, and many have a safety latch as well.
• Barrel or screw clasp. Two small halves that screw together. It makes a strong, discreet join that almost disappears into a fine chain. The drawback is that it needs two hands to open and close.
• Bayonet clasp. Push the two ends together and twist. It gives a secure, streamlined join, but some people find it awkward to operate.
• Padlock clasp. A small, decorative lock that both ends of the piece loop over. It is heavy, suits heavier chain bracelets, and is often paired with a short safety chain as a back-up.

Magnetic clasps

A magnetic clasp hides a magnet in each end. Bring the two ends close and they find each other and snap together. There is no lever to find, no ring to aim at, and nothing to pinch, which is why a UK findings supplier recommends them for anyone who finds small catches difficult, such as people with arthritis or stiff fingers.

The trade-off is security. A magnet holds by attraction alone, so magnetic clasps are usually recommended for light and medium pieces rather than heavy ones. Some are made with a secondary catch for that reason.

Slides and multi-strand clasps

• Slide clasp. Both ends of the chain pass through a bead with a silicone insert, which grips them. Slide the bead up or down and the length changes, which makes it handy when you don't know the wearer's size. It needs a chain with enough body for the silicone to grip, such as a snake or box chain.
• Multi-strand and tube clasps. Built to fasten several strands at once and keep them in order, so layered pieces stay aligned instead of twisting together. If you wear several separate chains, How to layer necklaces has more on keeping them apart.

Remember that a necklace's length is measured with the clasp included, and that an extender chain fitted beside the clasp lets one necklace be worn at more than one length. Both are covered in Necklace lengths: a complete guide. Earring backs are a family of their own, covered in Types of earring.

Choosing a clasp

There is no single best clasp, only the right one for the piece and the person. The table gathers what the trade guides listed at the end say about each.

• For everyday wear, a lobster clasp is the usual choice, with a bolt ring on finer chains.
• For limited dexterity, a magnetic clasp is the usual recommendation, with a large toggle as an alternative that has no magnet. Small bolt rings and barrel clasps are harder to manage.
• For a valuable or formal piece, a box clasp with a safety catch, or a padlock with a safety chain, adds a second line of defence.
• For a gift where you don't know the size, a slide clasp or an extender gives some room either way.

The part that lasts

The pearls on the V&A's necklace are the newer part, and the clasp, with its square emerald, is the older. Somebody chose to keep it, fit it to fresh strands, and carry on. That is the quiet compliment a good clasp earns. You stop thinking about it, because it simply opens when you ask and holds when you don't.