The snaffle is constructed to work laterally and the curb
bit is made to work vertically. The combined
bits and the gag bits were made in an attempt to combine the two actions.
In dressage variation one has solved the problem by using
both bits at the same time in the horses mouth, and this is also quite common in
driving. This is really the only effective way to get the right actions of both
types of bits. However the use of two bits and two sets of reins require a rider
that is well coordinated, a novice rider would not be able to use such a
combination properly.
A lot of bits are made as “long shank
snaffles”, a jointed mouthpiece with shanks, like the Tom Thumb. However these
bits will put pressure on both sides at the same time when one takes a hold of
one rein :
The snaffle works so that
when one takes a hold of one rein the ring on the same side gets lifted away
from the corner of the horses mouth, giving release. The bit then slides through
the mouth, and the pressure comes on the opposite side which the horse yields
from.
But when you put shanks on
a jointed bit that is loosely attached to the bit rings, and place the reins on
the bottom of the shank the pressure effect gets changed. The looser the bit is
made - the more movable pieces - the worse this effect will get. As you tighten
one rein the bottom of the shank gets lifted away, but the top of the same shank
will get pushed into the side of the horses mouth creating pressure on the same
side as you are applying the rein.
The bit then slides through
the mouth and creates pressure on the opposite side too, as well as pressure to
the horses tongue and bars. In addition the chain, when used, gets tight under
the horses jaw and some pressure is placed on the horse poll.
In effect the horse is
getting pressure on all sides on its head at once making it hard for it to
understand which way it really is supposed to yield. Even worse are the ones
that are also combined with the mechanical Hackamore, then the horse also gets
pressure on top of his nose. There are not many horses that are comfortable in
such a bit!
Gag bits is a variation of
combined bits. Here the reins runs through the rings of the bit itself and are
attached to the side pieces of the headstall or directly over the horses poll.
Some even goes so far as having a steel wire go over the horses poll to give the
horse a sharp pressure there to get it to lower his head.