Here is a incomplete list of gag styles. Many gags can be combined with more elaborate head harness.

Ball gags (or ball gags) are one of the most traditional gags for humans. A ball is inserted into the mouth, held in place by thin straps around the face. The diameter of the ball depends on the wearer and the comfort level required. The balls come as small as 1” (2.5cm) and go up to over 3” (7.5cm). The most comfortable size for most people is somewhere between 1 3/4” (4.25cm) to 2 1/2” (6cm). Depending on size, they make it difficult or impossible for the wearer to talk. Ball gags also often come with more elaborate head gear to keep the gag in place. Some ball gags, often seen in Japanese bondage, do not use a solid balls but ones that have holes in them, allowing the wearer to breath and drool. Other ball gags feature soft balls, allowing the wearer to chew on the ball a little. This can help when you experience jaw-lock.

Inspired by the bits horses wear, these gags very popular among pony play enthusiasts. Bits do not prevent speaking, breathing or drinking and can usually be worn fairly comfortable for longer durations. They also, especially when combined with head gear, allow the wearer to be easily and comfortably guided. Many dominants also enjoy bits for humiliation since bit gags usually make the wearer drool.

Cloth gags are usually made of a long piece of fabric like a scarf. They are inserted between the teeth of and then tied behind the back of the head. Take care to not tie too tightly since that can cause injury to the corners of the mouth. Rough fabrics can also lead to chafing.

Dental retractors, also called dental ratchets, are commonly used in medical play. They originated in dental offices and are used there to hold the jaw open for dental surgery. They are made of two thin pieces of metal that run across the whole length of your mouth and have a ratchet on one or both sides to secure them. Because of the thin metal used, dental retractors allow the whole size of the mouth to be penetrated by other objects, i.e. in skull fucking.

Molt Retractors are another form of medical equipment adopted for kink. They are similar to Dental retractors but only reach half way across the mouth. Because of that, the metal molt retractors are made off is usually much stronger.

Mouth Springs are the smallest of the gags inspired by dental equipment. Usually only an half an inch (1cm) wide, they are usually not able to withstand the force of a person trying to close their mouth. They however work well to remind the submissive partner to keep the mouth open. If you want to use mouth springs to force the mouth to stay open, you can use two, one on each side of the mouth.

Like dental retractors, ring gags are designed to open the mouth of the wearer. This allows for breathing, noise and even penetration. Since the ring is usually wider than the metal used on dental retractors, oral sex requires a very large ring.

Tube gags are similar to ring gags but use a tube instead. The tube is often flexible to allow the wearer to bite down a little. The tube allows the dominant partner to force liquids (i.e. urine) into the submissive's mouth.

Funnel gags are very similar to tube gags but have a funnel. This makes it even easier to force liquid into the submissive partner’s mouth.

Penis gags are over the mouth gags (that means they cover the lips and parts of the chin and cheeks) that are usually made of leather or heavy rubber and have a penis shaped object for insertion into the mouth. Some penis gags also have a second penis (or O-ring) on the outside to penetrate a partner. This form of gag does not allow for breathing through the mouth.

Inflatable gags come in two forms. One is similar to penis gags, however the penis has been replaced by an inflatable bulb. The second form is just an inflatable bulb. This type of gag relies on inflation to keep the gag in the mouth of the wearer.

Tape gags are simply a piece of tape over the mouth. Very simple and effective, this gag can be combined with inserting an object like a ball, a sock or used panties into the mouth before taping it shut.

Muzzles are usually made of leather and are integrated with a head harness. They cover the mouth and chin of the wearer.

One of the major concerns with gags is breathing. Often, especially with congestion, relying on nasal breathing only is a bad idea. While it is generally considered careless to leave a submissive partner alone when gagged, it is even more problematic when using a gag that does not allow proper breathing.

Gags need to be cleaned before use. Do not use gags that have sharp edges or cracks in the plastic. Soft gags need to be check that no pieces can get lose and be inhaled.
Some people recommend that inflatable or penis gags be covered with condoms to keep them clean or add flavor. Others argue that this is a bad idea since the front teeth can easily cut the condom and the pieces can interfere with breathing or induce throwing up.

The size of the gag usually determines the duration it can be worn. The wider the mouth is opened, the shorter the duration before the gag becomes uncomfortable. Softer gags can be worn for longer times because they allow for motion of the jaw muscles. Gags that don’t allow breathing through the mouth are not recommended for longer wear.

The tension on the jaw muscles can easily induce jaw locking. If you’re prone to jaw lock, you should avoid large gags and if so, use very soft ball gags instead.

Some gags, especially those made of rubber, have a very distinct taste. Some people love this taste, for those that don’t, there is no known way to get rid of the taste completely. It is however possible to reduce the taste by washing the gag (remove any leather straps) in the dishwasher several times, soak in vinegar or vodka. Some forms of mouth wash are also supposed to work on some materials.