You want to put on your necklace, but the small spring ring clasp just won't catch. Before you keep trying behind your neck, try telling apart the "part that opens" and the "hole it goes through" on a desk. Where you need to look again depends on whether your fingers are slipping, you can't see the hole, or the clasp won't spring back.
Here we focus on the spring ring type, where a small tab opens part of the ring, and go over the checks before wearing and how to fasten it. The same steps do not apply to magnetic, push-in and other types. Follow the instructions for your own piece, and proceed without bending the clasp or pulling the fine chain.
1. Tell the tab of the spring ring from the hole on the other side

First, with the necklace taken off, lay both ends on a bright desk. A spring ring has a round ring on one side with a small tab; moving the tab opens part of the ring. Even if it looks round, if it is a twist-off type or uses a magnet, do not try the spring ring operation.
Check the opposite end as well. It may have a plate with a small hole, a round ring, an adjuster chain, and so on. What you fasten to is not the outer edge of the decoration but the hole specified for your piece. Rather than memorizing the shapes on the left and right, distinguish the "side that moves" from the "side you pass through", and you will know which places your fingers must not cover.
On a spring ring, look at the tab, the opening, and the part connected to the chain separately. If the gap in the ring is hard to see because of reflected light, change the angle a little on the desk and check again. There is no need to spread the metal ring or push a fingernail or needle into the joint to find the gap.

If a plate has two holes, or there are rings along the chain, not all of them are necessarily the fastening position. To avoid mixing up the small parts that connect the adjuster ring and the main body, check against the included diagram or the explanation from when you bought it. While you are unsure of the position, do not hook onto a fine ring that happens to catch your eye to set the length.
If you are not sure whether there is a movable tab, or the spring ring differs from the one in the explanation, stop and check the model number or the type of clasp. A way of fastening that worked on another necklace may not be usable as it is. Narrowing down the structure first is preparation that saves you from fumbling behind your neck again and again.
Even if the visible hole seems big enough, the thickness and angle of the clasp can keep it from going through. Do not decide whether it fits by size alone; check in the next step whether it passes through easily in that combination. If the parts may have been mixed up, do not try to solve it with force.
2. On a flat surface, check where to hold with your fingers and the clasp

Choose a flat desk where parts are easy to find if they fall. Set out just one necklace and a shallow tray, and move other chains out of the way first. If it is hard to see your hands, use a mirror that stands stably or a light at hand. Avoid handling small clasps near a drain.
If your hands are wet, or slippery from cream and the like, it becomes hard to keep hold of the tab. Get your hands in order first, and deal with any dirt on the necklace as the material's instructions say. Putting oil or adhesive on the clasp to make it easier to fasten is not part of everyday handling.
On the plate side, support a part without a hole so that the hole stays visible. If you cover the whole plate with your fingers, you will have to look for the place to pass through again even after you bring the spring ring close. When the other side is a round ring, too, change where you support it a little so your fingers do not block the space to pass through.

On the spring ring side, support the body and place a finger where you can move the tab. Don't fix on one combination of holding fingers; look for a position where you can handle it without hiding the opening. Don't try to force the clasp open by hooking it hard with just your fingertip, and stop if a way of holding hurts your nails or fingers.
Place the chain on the desk with some slack and look only at the clasps at both ends. If you try to open the spring ring while the chain is taut, it is easy to put extra load on the small parts. Also check that the pendant is not hanging over the edge of the desk, so the clasp is not pulled by its weight.
When you are ready, first without bringing the other side close, move the tab within the specified range and see whether it returns. If the movement suddenly becomes heavy, it does not return, or the shape of the ring has changed, hold off wearing it that day. Don't operate it hard again and again thinking that repeated movement will fix it.
3. Pass it through the hole, release the tab, and look at the closed state

On the desk, face the two ends toward each other so that the hole in the plate and the opening position of the spring ring are visible. Move the tab to make an opening, and pass the spring ring through the hole on the other side. Don't stop at just pressing it against the edge of the hole; confirm with your eyes that the ring passes through the hole and is connected.
If it doesn't go through, let go before adding force and check whether your fingers are blocking the hole or the plate is tilted too much. Don't rush to hold the tab and bring the other side closer at the same time; line them up one step at a time on the desk. If the thickness of the clasp doesn't fit the hole, check the compatibility rather than widening the hole.
Once you have passed it through the hole on the other side, take your finger off the tab and look at the state where the opening has returned. Check that the chain or plate is not caught in the gap, and that no gap remains in the closing part. Even if it looks connected, if the other part is merely resting on the opening, fasten it again.
When checking, support the clasp in your hand and do not test its durability by pulling the chain hard. If it does not close when you release the tab, bites in at an angle, or comes apart when you let go, stop using it. Do not move on to tightening or crushing the ring with a tool, or adjusting the spring.
Even if you can fasten it on the desk, how it looks and where your arms are will change behind your neck. Next, check whether you can reach comfortably when putting it on. If the operation on the desk is still difficult, you can also choose a different necklace rather than hurrying to put it on and repeating the same operation.
When taking it off, too, support the clasp and operate the tab rather than pulling the chain to open it. See that the other side has come off the spring ring, then return both ends to the tray. Check not only the action of putting it on but also that you can take it off before you wear it.
4. Choose the position and length to suit the structure

Before putting it on, move your hair and collar aside so the clasp is not buried in strands of hair or fabric. When fastening behind your neck, hold the two ends one at a time so you don't lose track of them, and don't keep bending your arms or neck unnaturally. Don't try again and again in a position that is hard to reach, or pull the chain taut to make slack.
Fastening at the front of the neck and then moving it to the back is an option when the clasp and decoration can be moved without strain and there is enough length. It is not a method to recommend across the board for short necklaces, ones with fixed decoration, or ones that catch on clothes or hair. If you feel resistance, don't turn it around into place; take it off once.
For a necklace with an adjuster chain or rings, choose the specified fastening position while it is off. Look at whether the thickness of the clasp fits comfortably between the holes or rings, and check the closure as well. Having an adjuster chain is not the same as being free to hook onto any of the fine links.
Slide-type length adjustment is separate from the operation of fastening the spring ring. Support the specified part and move it in the direction given in the instructions. Do not adjust by pulling the chain while wearing it, or by pinching the spring ring and pulling the chain out.
If you use an add-on extender, first check which clasps it is compatible with and how to attach it. Some have a step of connecting the part to the receiving side of the necklace and a step of hooking the main clasp onto the extender side. Don't connect parts of different shapes just because the length would be enough.
Once it is on, check in your usual posture that there is no tightness or sense of being pulled. Whether the clasp holds and whether it is comfortable to wear are separate things to check. If the clasp turns to the front after wearing, you can sort it out with the steps for reviewing the necklace's structure and contact with the collar.
5. If it stays hard to fasten, separate the troublesome steps and choose again

If it feels difficult every time, sort out where you get stuck: "the tab is hard to open," "I can't keep it open," "I can't see the hole on the other side," or "I can't tell whether it has closed." Rather than changing everything at once, review one step first, such as changing only how you hold it on the desk, and comparisons become easier.
If you can do it on the desk but only wearing it is hard, don't assume the clasp is faulty; check how far your arms reach and where you can see. Conversely, if the tab doesn't return even on the desk, don't try to make up for it with practice at putting it on. Note separately whether the movement has changed from before and whether any part is bent.
If you ask about buying or repairing it, tell them a photo of the clasp you use and which step is hard. A bigger clasp does not always solve the problem. The hole on the other side, the thickness of the chain, and the overall length and weight also matter, so check the fit before swapping out a part yourself.
If you choose a different clasp, the direction of opening and closing and the operations needed will also change. Don't switch to another clasp without understanding how it works just because the current tab is hard to handle. Choose one after checking that it is easy to remove and that it can be used with your piece.
On a rushed morning, there is no need to put the same hard-to-handle necklace on again and again. You can choose another one that is easy to fasten and unfasten, or skip neck accessories for the day. Store the necklace you took off separately from other chains, without bending the clasp hard.
When a spring ring is hard to fasten, before using more force, start by separating the tab, the opening, and the hole on the other side where you can see them. Check opening and closing on the desk, put it on at a position that suits the structure, and finally look at the closure. Use this order to narrow down the difficult step, and if the movement seems abnormal, stop using it and check.