Gag

Gag Bit
The gag bit offers the same action as a snaffle bit with the addition of leverage pressure, what sets it apart from the pelham bit is that it is not used with a curb chain.

The amount of leverage and severity of the bit will depend upon the type and length of gag shanks and the mouthpiece chosen, and as with any bit the severity ultimately comes down to the riders hands.

Gag Bit Points Of Pressure
Gag bits have a lifting effect due to the leverage pressure and are well suited to strong horses prone to lowering their heads.

Corners
Bars
Tongue
Poll
Roof of mouth if a port is included
Side of Face if fulmer cheeks are included

Gag Sizes
Gag bits are measured from between the mouthpiece rings or shanks and are usually available in sizes ranging from 3, 3.5, 4, 4 1/4, 4.5, 4 3/4, 5, 5 1/4 , 5.5, 5 3/4 and 6 inches.

Gag Mouthpieces
Gag bits have several mouthpiece options available. As a guide thin or twisted mouthpieces are far more severe than straight bar wider mouthpieces which spread the pressure more evenly across the tongue, however each horse is different so you'll need to think carefully about what is going to be most comfortable for your horse as what works for one horse may be far from suitable for another.

Single Jointed - Mouthpieces with a single link in the middle produce a nutcracker action upon the tongue when the reins are used, causing one strong pressure point on the middle of the tongue.
Double Jointed - mouthpieces with two links such as a french link, produce two pressure points on the tongue over each link and depending on the shape of the central link a third point of contact there as well.
Multi Linked - Multi linked bits, such as the waterford offer several different pressure points across the tongue and often help to relax the horses mouth as these types of mouthpieces are not fixed so they often move around a little in the horses mouth and can help prevent the horse from taking hold of the bit.
Roller - Mouthpieces that contain roller segments again help to relax the horses mouth and encourage the horse to not lean on the bit and relax their jaw. Copper rollers in particular are great for also encouraging salivation.
Mullen/Straight Bar - Straight bar mouthpieces offer even pressure across the tongue, for horses with large tongues mouthpieces with a small port can allow more room for the tongue.
Twisted - Twisted bits are for experienced riders only due to their sharper action upon the tongue.

Gag Shanks
As a rough guide the longer the gag shanks and larger the snaffle rings are the more leverage pressure will be obtained:

Gag Snaffle - Gag bits such as the Balding or Cheltenham Gag have large rings attached to the mouthpiece similar in look to the rings of a snaffle bit, the difference is that the rings have two holes at the top and bottom through which the gag cheeks are passed and from which the reins are attached at one end and the cheek pieces at the other. When the reins are used pressure is applied to the mouthpiece causing the bit to lift up in the horses mouth and cause pressure to the poll, tongue and corners of the mouth.
- Cheltenham Gag - The rings of a Cheltenham are fixed to the mouthpiece in a similar way to an eggbutt snaffle.
- Balding Gag - The rings of a Balding Gag are loose through the mouthpiece helping to prevent the horse from leaning or taking hold of the bit.
American Gag - The American gag has a sliding shank that attaches to the mouthpiece. The shank has a loop from which a snaffle rein can be attached and a ring at the bottom for the second rein to be attached offering greater leverage action.
Continental Gag - The continental Gag has a shank of rings and offers varying amounts of leverage depending on the setting chosen. The uppermost ring is the cheek piece attachment and below this is the snaffle ring, which is the largest and which attaches directly to the mouthpiece. Below the snaffle ring are two further rings, with the lowest ring offering the most amount of leverage. The continental can be ridden with either one rein or two and can aid in lowering the horses head.
Fulmer Gag - There is also the addition of having Fulmer cheeks extending above and below the bit rings, providing side face pressure which helps to increase turning and general control.

Materials Gaga Are Made Of

Stainless Steel
Stainless steel bits are long lasting and silver in appearance, with the majority of horses going very well in them.
Cupro Nickel And German Silver
Light gold in color, the taste encourages the horse to relax their jaws, mouth the bit and salivate.
Copper
Copper encourages the horse to relax and salivate in its mouth due to the warming nature of the metal.
Sweet Iron
Sweet Iron gives the horse a sweet pleasant taste in its mouth and encourages salivation and relaxation of the mouth.
Rubber and Plastic
These are gentle on the mouth and flexible in design. Some rubber bits can be a little chunky and so do not suit horses with very small mouths or large tongues.