Clasps or jewelry fasteners have been an integral part of jewelry ever since it is being worn. While their basic function has been to secure jewelry in place, today clasps have evolved as a fashion statement too. Besides the regular designs, one can now avail of an entire array of decorative, bejeweled and bold clasps. These can either be internal or external depending upon the bracelet style. For example, most bangle bracelets have clasps on the inside. Here is a more detailed overview on the prevalent range available in markets.
Barrel clasps
Hook and eye clasps
S hooks and S clasps
Slide lock clasp
Magnetic clasps
Hidden clasps
Toggle clasps
Lobster claw clasps
Box clasps
Spring ring clasps
Decorative clasps
Other clasps and clasps for ear rings

Barrel clasps
These are barrel shaped with each half of the barrel secured to either side of the jewelry. The two halves fit together to secure the clasp through a tiny screw mechanism. While magnets may also be used to secure a barrel clasp, screws are considered a safer option. A variety of designs are available in barrel clasps, which can also be embedded with a range of diamond shapes or semi-precious stones to add to the look of the jewelry.
Pros: Attractive and simple, does not hinder the look of jewelry.
Cons: Can be difficult to operate if the screw does not fit properly. May come unscrewed.

Hook and eye clasps
One of the simplest clasps available in the jewelry market today, these operate on the principle that the hook on one side of the jewelry fits into the eye on the other end. While the hook resembles any ordinary hook, the eye may be in circular or may also be shaped like the figure 8. The clasp is easy to operate and also keeps the jewelry secure. Moreover it is easy to manufacture and a thick wire is all that is needed to prepare it. Such fasteners are ideal for heavier jewelry like detailed necklaces as the weight of the jewelry helps to keep the hook securely in place.
Pros: Easy to make and simple to use.
Cons: May slip off if not secured properly.

S hooks and S clasps
These are the most basic forms of clasps and have been prevalent for a long time. Here, the hook/clasp is shaped like the letter S and it fits into a circular ring on the other end. Most vintage necklaces , bracelets and other jewelry pieces feature these, in both simple and elaborate styles. The reason for their prevalence is their ease of manufacture and ease of adding to any form of jewelry.
Pros: Easy to manufacture, inexpensive and easy to repair.
Cons: May slip off easily, thus do not provide much security for expensive jewelry.

Slide lock clasp
Also known as the tube bar clasp, in this mechanism, one side of the tube is grooved while the other end has slots. When the two parts are slid together, the clasp secures and stays in place. This can also be opted with magnetic features to make it more secure. To open a slide lock clasp, users need to hold either side of the clasp and pull.
Pros: Works well for multi-strand chain bracelets or necklaces.
Cons: May be difficult to operate as it needs nimble fingers.

Magnetic clasps
Relatively new in the market, magnetic clasps work with the help of magnetic charges where the opposites attract and adhere to each other. Due to their ease of operation, these have become increasingly popular and many opt for it. In order to strengthen the clasp, some forms of jewelry also offer the option of turning the clasp 90 degrees after one has snapped the two ends together.
Pros: Extremely easy to operate and ideal for people with arthritis.
Cons: May not secure jewelry popularly if magnets are weak. Not suggested to be worn by pregnant women, near computers or while wearing pacemakers; as heavy magnetic charges may interfere with other devices.

Hidden clasps
As the name suggests, these are hidden from view and do not obstruct the beauty of the jewelry. For example, in the case of tennis bracelets, where the wearer would prefer the line of diamonds to be continuous, hidden clasps are ideal to keep the jewelry in place and also provide a beautiful and complete bracelet. They usually have a large head on one side of the clasp that engages into position once the clasp is latched on. As the head of the clasp has a design similar to the bracelet, the clasp seems to disappear once it is latched on. A safety latch is provided for added security.
Pros: Unobtrusive and does not disturb the look of the jewelry.
Cons: May be difficult to operate due to low visibility.

Toggle clasps
This popular and basic type of clasp comes with a circle or a square ring on one end and a long bar shaped like a T on the other end. The bar fits into the latter and gets held in place. While toggle clasps are sturdy and do not slip, many do not opt for it due to its hardy look that may not go well with delicate jewelry. There is also another end of the spectrum, where many buyers use toggle clasps as an attractive and decorative element of the jewelry. While purchasing a bracelet with a toggle clasp, do ensure that you add a few centimeters to your wrist measurement, so that the toggle can easily be maneuvered into the ring.
Pros: Easy to use and repair. Simple and elegant in appearance.
Cons: Can hinder the look of delicate jewelry. Can slip off if the T bar is not long enough.

Lobster claw clasps
Also known as parrot clasps or trigger clasps, the general look of the clasp lends to its name. It has a tiny spring mechanism that keeps the arm of the clasp closed till one pushes the lever to open it. These are easy to open and close independently as compared to other mechanisms. Moreover as they keep the jewelry secure, many prefer it over other clasps. Before purchasing jewelry that has such a clasp, do ensure that it operates properly and snaps back easily. This clasp is ideal for heavy jewelry and can be opted in a variety of shapes like heart shape or dolphin shapes.
Pros: Attractive, secure and easy to use.
Cons: May prove expensive than other clasps. Smaller clasps may need nimble fingers to operate.

Box clasps
Here one edge is fashioned like a box with a slit and the other clasp is fashioned like a sheet of metal known as the tongue. The box part of the clasp may have grooves or notches while the tongue is usually a folded sheet of metal that forms a spring lever. The clasp opens when you push down on the outer side of the flat metal. To close, the wearer needs to slide the metal wedge inside the box where it clicks into place. Today many designers are using large box clasps for necklaces and bracelets. In the former case, these are meant to be worn in front, like a pendant. In such cases the clasp is decorated with filigree work or is accentuated with gemstones. Smaller and plainer clasps are usually worn behind the neck. While these clasps are pretty looking and decorative, they are often not as secure as lobster claw clasps. If you wish to opt for a box clasp, you can take the option of added security with a safety guard.
Pros: Offers freedom of design and creativity. Easy to operate
Cons: Not very secure for expensive jewelry, and needs security chains.

Spring ring clasps
Quite popular in bracelets, necklaces and anklets, these clasps operate with the help of a little spring mechanism inside the clasp. To open, the little lever on the ring needs to be pushed back. It can be fitted back by inserting the loop on the other side of the bracelet into the spring ring which snaps back to place once the lever is set free. These are also commonly used for securing charms to bracelets.
Pros: Highly secure form of clasp. Also preferred for its subdued look that does not overpower the look of the jewelry.
Cons: Needs extremely nimble fingers to operate. May not be suitable for those with arthritis, joint problems or weak eyesight.

Decorative clasps
Depending upon the style of jewelry, many designers also offer decorative clasps. Such clasps form an important part of the jewelry design while also holding the jewelry securely in place. Decorative clasps come in one of the above styles and have distinctive shapes. These can further be accentuated with the help of filigree work or embedded gemstones.
Pros: Enhances the look of the jewelry, along with functional advantage.
Cons: May be difficult to repair or replace at ordinary jewelry stores, in case clasp is spoilt.

Other clasps and clasps for ear rings
Besides the above range of clasps, there are a host of other styles also available. The screw model clasp allows for a small screw to fit into the notches in the two ends of a bracelet. Fold-over clasps are popular for bracelet styles too where the top half of the clasp folds over and is pressed down on the bottom half of the clasp. Certain bracelets also offer the option to tie the two ends together for securing the jewelry. Besides this, diamante clasps, press stud, button and loop and snap on clasps are also popular.  An entirely different array of clasps are also available for ear rings. The screw model clasps are popular for heavy ear rings, where a small nut fits onto the delicate threads of the screw. The fish hook model, magnetic clasps and clip ear rings are also popular for ear rings. Hidden clasps that do not obstruct the beauty of design and tube clasps (where a thin tongue fits into a tube) are also popular styles for ear rings.

Clasps are an important finishing touch to any jewelry, so choose with care as the attractiveness of the jewelry will depend upon it. While you ensure that it keeps your jewelry secure, also see to it that the clasp is easy to operate and can be easily repaired, if the need arises. Choose the metal of the clasp with care, such that it is sturdy enough and can easily be replaced too if the need arises. If you are getting your jewelry customized ask for a clasp that is easy to put on and remove as certain clasps offer restricted use. Finally do keep in mind that it gels well with your jewelry and does not make the entire jewelry look ugly.