A Lobster Clasp is usually slightly elongated, with a spring hook that opens a small piece of metal to allow the clasp to fit through a ring, with the metal closing once the spring is released, to ensure that the clasp is secure.
A Bolt Ring is like a lobster clasp, but the fitting is circular instead of elongated. The mechanics are similar in that a small piece of metal acts as a lever to open the clasp – in this case, the metal across the opening rotates inside the ring enclosing it, rather than lifting as it does with a lobster clasp.
These clasps are sold in a variety of metals, so pick the one that is most suitable for your project. They are also available in a range of sizes, so if you are buying from a website, take care to check the information and make sure that you are buying the size that you expect. The sizes are given in millimetres usually and refer to the actual size of the ring in the case of a bolt or the length of a lobster clasp. Depending on the retailer, these clasps may be sold with or without the eye through which they will need to fasten. If you are buying a pack of clasps that have no eyes to go with them, then you will need to buy a closed ring (or possibly jump ring) to go with your clasp so that it can be fastened. As with the clasps, the rings also come in a variety of sizes, so make sure you buy something that is a similar size to your clasp or it will look very odd!
Pros: Once fastened, these types of clasp tend to be very secure as there is no danger of the ring falling out of its fastening. Both lobster clasps and bolt clasps are widely available, frequently used in commercial jewellery and can be bought very cheaply.
Cons: I find that both lobster clasps and bolt clasps can be a little fiddly to use, especially if you pick a smaller size. They can be particularly fiddly on bracelets, where you are trying to open the spring and hook it through the loop one-handed. Unless you buy very high quality, the spring fixture can break after a relatively short length of time, so the clasp (and possibly also the jewellery) is rendered useless.